Instant reply in sports

Association football
Goal line technology

The Cairos system involves embedding thin cables in the turf of the penalty area and behind the goal line. The electrical current that runs through the cables generates a magnetic field. A sensor in the ball measures the magnetic fields as soon as the ball comes into contact with them and transmits data about the ball’s location to receivers located behind the goal that relay the data to a central computer. [https://2.bp.blogspot.com/-fKco15BfSK8/T7-WnFmI-EI/AAAAAAAABHk/-Vjsq-BGuWc/s1600/Goal+line+technology+brought+in+for+England+friendly+at+Wembley+2.png The computer then determines whether the ball has crossed the goal line. If so, a radio signal is transmitted to the referee’s watch within a split second. The implantation of a chip suspended inside the ball has no impact on the ball's characteristics. Players will not notice the difference between a ball with an implanted chip or a ball without the chip, and the ball is specially designed with suspended sensor inside it, so it can withstand vigorous kicks and the chip will always be in the middle.]

Video Assistant Referee (VAR)

VAR is used for the following:
 * Goal (player reviewed only)
 * Penalty (player reviewed only)
 * Direct red card offences (VAR reviewed only)

A player review must be called within 20 seconds of an incident with a 'T' sign. Afterwards, the referee signals an on field review (OFR) by making the outline of a rectangle, indicating a video screen. The OFR takes place in a designated referee review area (RRA), adjacent to the field of play and in public view to ensure transparency. Slow motion replays are only used to establish point of contact for physical offences and handball, while full-speed replays are shown to determine the intensity of an offence or whether a handball occurred in the first place. During an OFR, the VAR transmits several video replays from different camera angles to allow the referee to make their decision. Once an OFR is completed, the referee makes the TV signal again, before indicating the decision made. If the ball was out of play, it restarts with either the original decision or the new decision if the on-field one was changed. If play was stopped to conduct an OFR and the decision was not changed, a dropped ball occurs.

In matches using VARs there must be a video operation room (VOR). The VOR is where the video assistant referee (VAR) and replay operator (RO) work, and is usually in/close to the stadium. Only authorised persons are permitted to enter the VOR or communicate with the VAR, and RO during the match. More info is in the VAR protocol booklet. A player, substitute, substituted player or team official who enters the VOR will be sent off.

[https://football-technology.fifa.com/media/172055/blog_tv_gfx_1.jpg During the VAR process, there will be a picture-in-picture solution with 3 boxes displayed to the TV audience and on the stadium screen to the stadium fans. Box 1 is showing replay of the incident being review (basically what the referee is exactly looking at on the RRA screen), Box 2 will show the referee him or herself at all times and Box 3 will show the VOR. The bottom left graphic will explain what is being reviewed.]

The offside technology – which is integrated into EVS’s Xeebra VAR system – uses machine learning to automatically calibrate the field of play, and a mutli-camera review feature enables an offside line to be overlaid for VAR operations during matches. It received FIFA’s Quality Programme for Virtual Offside Lines (VOL) after EVS went through 2 independently run testing events in September 2018. It was tested using 40 different match situations, with 8 cameras determining the accuracy of the offside line. The tests examined both the 2D positioning of the offside line and the 3D body positioning of the players. There's no need for pre-game setups.

Baseball
In Major League Baseball, instant replay has been introduced to address "boundary calls", which include questions on whether or not a hit should be considered a home run (HR). Among reviewable plays are: Fair Ball-HR; Foul Ball, Ball Clearing Wall-HR; Ball Staying in Play-Live Ball; Ball Leaving Field of Play-HR; and, Ball or Player interfered with by spectators (called Spectator Interference). The latest MLB collective bargaining agreement, pending agreement by the umpires' union, expands instant replay to include: Fair Ball; Foul Ball along foul lines, or Ball Caught for Out; Ball Trapped Against Ground or Wall; as well as expanding Interference calls to all walls regardless of whether it is a "boundary call" or not.

In Little League Baseball, Instant Replay was initially adopted for the Little League World Series only but later was expanded to include the qualifying regional tournaments as well. It includes all "boundary call" plays reviewable at the Major League Level, in addition to adding review to plays involving force outs, tag plays on the basepaths, hit batters, and for defensive appeals regarding whether a runner missed touching a base.

Badminton
BWF introduced Hawk-Eye technology in 2014 after testing other instant review technologies for line call decision in BWF major events. Hawk-Eye's tracking cameras are also used to provide shuttlecock speed and other insight in badminton matches. Hawk-Eye was formally introduced in 2014 India Super Series tournament.

Basketball
In NBA basketball, the officials must watch an instant replay of a potential buzzer beater to determine if the shot was released before time expired. Since 2002, the NBA has mandated installation of LED light strips on both the backboard and the scorer's table that illuminate when time expires, to assist with any potential review.

Instant replay first came to NBA in the 2002–03 season. In Game 4 of the 2002 Western Conference Finals, Los Angeles Lakers forward Samaki Walker made a 3-point field goal from the half court at the end of the second quarter. However, the replay showed that Walker's shot was late and that the ball was still in his hand when the clock expired. The use of instant replay was instituted afterward.

Beginning with the 2007–08 season, replay also can be used in determining players being ejected from contests involving brawls or flagrant fouls. In the 2008–09 season, replay may also be used to correctly determine whether a scored field goal is worth 2 or 3 points. It may also be used to determine the correct number of free throws awarded for a missed field goal. It may also be used in cases where the game clock malfunctions and play continues to decide how much time to take off the clock. In 2014, the NBA consolidated its replay work in remote instant replay centre to support officials in multiple games.

In college basketball, the same procedure may also be used to determine if a shot was released before time expired in either half or an overtime period. In addition, NCAA rules allow the officials to use instant replay to determine if a field goal is worth 2 or 3 points, who is to take a free throw, whether a fight occurred and who participated in a fight. The officials may also check if the shot was made before the expiration of the shot clock, but only when such a situation occurs at the end of a half or an overtime period. Such rules have required the NCAA to write new rules stating that, when looking at instant replay video, the zeros on the clock, not the horn or red light, determine the end of the game.

In Italy, host broadcaster Sky agreed with Serie A to the adoption of instant replay for special tournaments and playoff games, and in 2005, for the entire season. Instant replay would be used automatically in situations similar to the NCAA, but coaches may, like the NFL, have one coach's challenge to challenge a two or three point shot. Officials may determine who last touched the ball in an out-of-bounds situation or back-court violations.

The adoption of instant replay was crucial in the 2005 Serie A championship between Armani Jeans Milano and Climamio Bologna. Bologna led the best-of-five series, 2–1, with Game 4 in Milan, and the home team leading 65–64, as Climamio's Ruben Douglas connected on a 3-point basket at the end of the game to apparently win the Serie A championship. Officials, knowing the 12,000 fans on both sides would learn the fate of the series on their call, watched replays of the shot before determining it was valid.

The Euroleague Basketball (company) adopted instant replay for the 2006 Euroleague Final Four and made a rule change determining the lights on the backboard, not the horn, will end a period, thus assisting with instant replay.

On April 6, 2006, FIBA announced instant replay for last-second shots would be legal for their competitions.

"The referee may use technical equipment to determine on a last shot made at the end of each period or extra period, whether the ball has or has not left the player's hand(s) within the playing time".

Before the beginning of the 2013-2014 NBA season, new instant replay rules were put into effect, saying that it can be used for: block/charge plays; to determine if an off-ball foul occurred before or after a shooting motion began in a successful shot attempt, or if the ball is released on a throw in. They also began to use instant reply to determine correct penalties for flagrant fouls.

Cricket
A Kookaburra cricket ball has an embedded microchip without changing the characteristics of the cricket ball itself. Sensors are placed at various hotspots in the playground, cricket ball, and in the shoes of the players. With the help of these sensors information about all aspects of the game is collected and sent to a central computer for further processing. The Computer collects the data, formats it for storage and stores it in a ways that it can be used for any purpose in the future. Data received from various sensors placed in the moving objects is processed and we get the distance of object from certain predefined point.

No ball: a triangular assembly of sensors by mounting 2 sensors statically in the crease and the 3rd one in the shoe of the bowler. Sensors in all the 3 positions talk to the central computer and communicate their (x, y) coordinates. Once they have the coordinates of the sensors, calculation the length of the sides of the triangle using distance formula are done and given:

𝑑 = square root of (𝑥2 − 𝑥1)2 −(𝑦2 − 𝑦1)2

The distance formula provides the lengths of all the 3 sides of the triangle and we can calculate the angles involved in the creation of the triangle using the formula given:

𝑥2 = 𝑦2 + 𝑧2 + 2𝑦𝑧cos𝜃

Here a check is made before calculating the angle, as we know that the length of the side which is labeled z, now if the side x gets smaller in length then the side z it give an automatic judgment of not being a no ball. If the angle θ is greater than 90o then it is assumed that the bowler has over stepped the popping crease line, indicating a no ball. Once a no ball is detected the system alarm for no ball and communicates it to the umpire

Stumping: Sensors in the batsman shoe, whenever the keeper collects the ball and hits the stumps with the ball in the hand ours system would check the sensor of the ball and the wicket are met such that it confirms that the ball had connected to the wicket and at the same time the system also checks the distance between the batsman foot and the wickets similar to the bowlers foot in the No-ball with the above Equations. Here a check is made before calculating the angle, as we know that the length of the side which is labelled z, now if the side x gets smaller in length then the side z it give an automatic judgment of not being out. If the angle θ is greater than 90othen it is assumed that the batsman has been out of the crease line, indicating stumped. Once this is detected the system alarm for stumped and communicates it to the umpire as well as to the scoring system [1]-[6].

Calculation of the ball trajectory for Leg Before Wicket (LBW): There's a special type of sensor which responds to nearby microwave radar, as the moving ball communicates its position to the receptor once every 100th of a second. So there's quite enough amounts of data about the movement of the ball, which can be used to calculate the parabolic curve of the ball traveling across the wicket. Trajectory calculation can be precisely done on the basis of points obtained from the previous motion of the ball in the prescribed plane. The trajectory is an excellent method for making decisions but there are at situations where the trajectory may be mis-interpreted and a wrong decision can be implied to the batsman because the batsman is not out if the ball pitches in the line and hits the pads. There are some other factors to be considered such as: These are some important factors to be considered by us when we make the decision. Accurate Decision can be made by us by using the sensors available in the ball, wicket, batsman shoes, pads and bat. Whenever the ball hits the batsman pad our proposed system observes various factors before making a decision such as: These questions are answered by the system by which our decision is made easier and accurate. The system answers the 1st factor by detecting weather the ball had any contact with the bat. It is processed with the sensor available in the bat and ball, if they are connected there is a signal informing us that the ball had connected with the bat it is nothing but the deflection obtained from the bat sensor. The 2nd factor is answered by our No-ball decision system which communicates to us if it is a No-ball. The 3rd and 4th factor are calculated by the system with the Distance between the 2 points i.e. using Equation 1 and 2. Let the Sensor in the wicket is recorded as X and the place where the ball had landed in the pitch is Y now we calculate the distance and deflection between these two points and another point Z is considered where the ball had hit the batsman pad using the ball sensor now again using the Equations-1 &2 we calculate the distance and Deflection of the ball with respect to the mid –stump. The value θ will provide us that the ball is deflecting either right or to left at first position Y to X. Again the θ value is calculated for the points between X and Z this deflection provides us that weather the ball is moving away from the stumps or into the stumps and we can also calculate that the ball will hit the stumps or not. The 5th factor is also addressed by the system by considering the sensor of the stumps and the impact of the ball that had hit the stumps. Again by using the Equation-1 we can get the Height of the ball and if the height is less than the height if the stumps we can assume that the batsman might be out by considering the various factors. The last factor can be addressed by our system by pointing the batsman position when the ball had hit his pad and also the position of the foot where the ball had hit the pad. We can also calculate the distance between the Foot and the stumps to identify that the batsman was in the line or crossed the line. By considering the above 6 factors we can make a decision in 3 steps: If the output from the 3 stages in ONE then our system declares that the batsman is out. Both the systems provide accurate decisions.
 * 1) Where did the ball hit the Batsman?
 * 2) What is the height of the ball?
 * 3) What is the trajectory of the ball?
 * 4) What is the position of the batsman?
 * 1) Did the bowler bowl a no ball?
 * 2) When the ball hits the batsman's pads, first the system identifies whether the ball had hit the batsman pad directly (no edge from the bat)
 * 3) What is the deflection of the ball from the Midstump?
 * 4) What is the height of the ball?
 * 5) What is the position of the batsman foot when the ball had hit the batsman pads?
 * 1) If the system output is 1 (i.e. ball had directly hit the batsman pad and the ball is not a No-ball).
 * 2) Here again if we get the output from the system as 1 i.e. the ball had been in the path and the deflection is into the stumps and the height of the ball when it hit the batsman pad is below the height of the stumps.
 * 3) If the output is again 1 from the system i.e. the batsman position is in the path and near to the stumps.

Runout: The most common way where any one of the batsman at the ends can get out. A run out is accepted even for a No Ball. The run out decision generally in the game of cricket is made by the umpires in the field and the third umpire also. At some stages in the game the run outs are made to be crucial decisions for the umpires to make a decision. For an effective decision to be made by an umpire he requests the 3rd umpire and he gives the decision by using the cameras available round the ground and in the ground. This is also not an easy task to be considered by the 3rd umpire as the technology may not be helpful in making clear decisions. These issues can also be answered by our system in affective manner. The input required to make the decision are: With these inputs loaded into the system and other inputs such as sensors available in the ball, wickets, bowlers and other player’s sensors are used in making the decisions. To differ stumping from run out 3 sensors are placed along the pitch where the batsman has to run. 2 sensors are placed away from 5 yards to the stumps at both the ends. Another sensor is placed in the halfway of the pitch to record that the batsman had attempted to run. The system makes decisions in the following steps:
 * 1) Has to record the Batsman sensors available in their shoe and bat.
 * 2) If any substitute is provided for the batsman his sensors are to be recorded along with the other people.

1) When the ball hits the stumps by any player in the ground our system detect from where the ball is thrown.

2) If the ball is thrown by any player other than bowler and if the batsman bat or leg is not grounded in the crease at any end the batsman running at that end is considered as run out.

3) If the bowler makes the attempt it has a certain criteria to make the decision.

In the above described 3 steps our proposed system makes decisions. The 1st is used by the system to record which fielder had thrown the ball to the keeper /bowler. The 2nd step is that when the ball connects to the stumps if the batsman leg or bat must be in the crease. This is calculated using the mid-stump sensor and batsman leg/bat sensor. When the bowler/keeper collects the ball from fielder and hits the ball to the stumps at any end, the sensor of the ball and the stump will get connected that is considered as the input to make decision. At that time in that end the batsman sensors of leg & bat both distances are calculated using the Equations 1&2 if both the distances are greater or equal to the distance of the crease the batsman running to that end is declared as Run out. If the ball doesn’t connect to the stumps even if the batsman is out of the crease he is considered as not out. The distance of the sensor is calculated when they are grounded only. The 3rd step is a special case i.e. if the bowler attempts to out the batsman at non-striker end without delivery or on a straight drive occasion. In these 2 situations there are chances where the non-striker is out. In the first situation i.e. when the bowler attempts to deliver the ball and if he attempts to out the batsman the ball has to be touched to the ground and then he has to hit the stumps. Here we would weather the ball had touched the ground by using the sensor available in the ball. If the batsman is away from the crease he is out. If the batsman drives the ball and if the bowler collects the ball and hit the stumps and if the non-striker is away from the crease he is declared as out. Here our proposed system would check whether the ball had any contact with the bowler and hit the stumps. It can be identified by the system using the sensor in the ball and the deflections of the ball. The Proposed system declares a batsman as run out if the batsman bat and leg sensors distance is greater or equal to the distance of crease to stumps. If any of it is shorter he is considered not out only when the batsman leg / bat sensor are recorded at the 3 sensors this is considered when the batsman misses his bat while running.

Boundary Line Decision: The boundary line decision also a crucial decision for the umpire to be taken at times in a match. Generally in the game of cricket the boundary line is the outer line of the cricket ground generally placed far away with a distance around 90meters from stumps. So the decision whether the ball had gone to the boundary or not is an issue to be discussed in some scenarios of the game. When the batsman strikes the ball and if the ball had touched the boundary line or if the fielder who is fielding in the ground makes contact with the ball and the boundary line it is to be considered as a boundary. At times the chase might end with a close call where the fielder might have contact with the ball as well as the boundary line. The 3rd umpire might not be able to make a clear decision. If we place sensors around the boundary line the system can provide us the accurate decision. The issue can be answered by our system in the following manner: Critical Catches: A famous quote is made by legends of cricket as “Catches Win Matches”. That is the important of a catch which can change the course of the match. At times the decision becomes critical for the field umpires and also to the 3rd umpire. The catches that are taken near to the ground called as Dive catches which are critical to judge. The system solves this problem in a much simpler manner. Whenever the umpires request the system our system checks weather the ball had made contact with the ground or not if not, the decision is out else not out. Our proposed system will make the decision by using the sensor available in the ball if the ball had made contact with the ground our system will identify it easily. In this manner our proposed system will help the Umpires in the game to make accurate decisions.
 * 1) If the ball gets contact with the boundary line it is declared as a boundary. This is known to our system with the sensors available in the ball and round the ground if the ball contact with the boundary line, our system immediately passes the message to us.
 * 2) If the fielder had made contact with the boundary line then our system passes the message to us and if the fielder dose have contact with the ball during that point of time our system passes us that the ball, fielder are in contact with each other and the fielder is in contact with the boundary line hence they are connected so our system passes message to us. The decision is made in 2 phases during the initial phase we identify weather the fielder or the ball had any contact with the boundary line using the sensors available in the ball and the fielder. If nothing is in contact it is not a boundary. If there is a contact then in the next phase our system identifies if the contact is made by the ball or by the fielder. If it is the ball our system declares it as a boundary. If it is the fielder our system checks the position of the ball either it is in contact with the fielder or not if yes it can be assumed as a boundary. If not it is passes a message as not a boundary. This decision is particularly a critical one during the day and night matches or at times during the game.

Wicket stumps

The stumps and the bails, known as a wicket, start flashing a luminous red if the bails are dislodged. The technology used is known as the Zing wicket system, the stumps and bails will flash the moment contact is broken. The bails are powered by hidden low voltage batteries. They each contain a microprocessor that detects when contact between the bails and the stumps has been broken. The bails are illuminated within 1/1000th of a second. "They can be vibrated, knocked, rained upon, but will only flash when both ends are completely dislodged from the stumps," explains Eckermann. The microprocessors then send a radio signal to the stumps which also light up.

Gaelic games
In Ireland, only a player can call for a review with a 'T' sign, if there should or shouldn't be a goal/over or if it should or shouldn't be a penalty. Both teams have 2 unsuccessful reviews. The posts automatically light up with LED lights and in different colours if the ball or sliotar successfully over the uprights and between the posts, using sensors inside the ball and inside the posts.

Gridiron Football
In American and Canadian football, instant replay can take place in the event of a close or otherwise controversial call, either at the request of a team's head coach (with limitations) or the officials themselves. There are restrictions on what types of plays can be reviewed. In general, most penalty calls or lack thereof cannot be reviewed, nor can a play that is whistled dead by the officials before the play could come to its rightful end.

American and Canadian football leagues vary in their application and use of instant replay review. In the National Football League, each coach is allowed two opportunities per game to make a coach's challenge, and get a third challenge if both of the original two challenges were successful. A challenge can only be made on certain reviewable calls on plays that begin before the two-minute warning and only when a team has at least one time-out remaining in the half. The Canadian Football League uses similar rules as the NFL, except the game has a three-minute warning near the end of each half instead of two. In NCAA football, each team only has one challenge per game, and gets a second challenge if the first one is successful.

U.S. high school rules prohibited the use of replay review, even if the venue had equipment that allows the practice, before 2019, when the National Federation of State High School Associations (NFHS) gave its member associations the option to allow its use in postseason games only. In Texas, where high schools have always based their rules on those of the NCAA, the University Interscholastic League, which governs public-school sports, allows its use only in state championship finals. The main governing body for Texas private schools, the Texas Association of Private and Parochial Schools, follows pre-2019 NFHS practice by banning replay review.

Ice hockey
The video goal judge reviews replays of disputed goals. As the referee does not have access to television monitors, the video goal judge's decision in disputed goals is taken as final. In the NHL, goals may only be reviewed in the following situations: All NHL arenas have a video goal judge, often officials in the Situation Room (also known as the "War Room") at the NHL office in Toronto make the final decision.
 * puck crossing the goal line completely before the time expired
 * puck in the net prior to goal frame being dislodged
 * puck being directed into the net by hand or foot
 * puck deflected into the net off an official
 * puck deflected into the goal by a high stick (stick above the goal) by an attacking player.

Review challenges

Beginning in the 2015-16 NHL season, instant replay reviews have been expanded to include a coach's challenge. Each coach receives 1 challenge per game, which requires the use of a timeout. Coaches may only challenge over situations whether the goal should have been disallowed because of goaltender interference or an offside, or whether a goal disallowed because of goaltender interference should be allowed instead. The challenging team retains its timeout and its challenge after every goaltender interference call that has been overturned. There are two situations that happen when a challenge is upheld: Challenges are not allowed during the final minute of regulation, as well as at any point during overtime. In this situation. However, for reviews that take place during coach's challenges, the on-ice officials determine the final ruling.
 * If an offside review is upheld, the challenging team receives a minor penalty for delay of game.
 * If a goaltender interference review is upheld, the challenging team loses its timeout.

Goal line technology

2 wide angle high-speed cameras are put at the top of the posts and in each side post to track the puck using a 3D software system to capture images of the position of the puck. If the puck completely crosses the red line an encrypted signal is send to the referee's watch within half a second to indicate a goal has been scored.

Rugby
Use of video referee by referees was introduced to rugby union in 1996. The laws of the game allow for "an official who uses technological devices" to be consulted by the referee in decisions relating to scoring a try. The decision to call on the Television Match Official (TMO) is made by the referee who draws the outline of a TV screen, then the call is made by the TMO, who takes his place near the press box or the Television Outside Broadcast van. He tells the referee by radio link-up the decision. Decision-making conversations between match referees and TMOs is broadcasted live to crowds in stadiums. The referee can consult referees only referred decisions if their on-field decision was that of a no-try, if a referee believes a try has been scored, TMO will review the play while the goal kick is being set up. They can then come over the top of the on-field call and tell the referee to pause the kick at goal if they believe they may need to reverse the try. TMO will also review yellow or red cards offences.

The captain of a team can also call for a review known as "captain's challenge". Only a captain or nominated co-captain can challenge a decision. Should the captain or co-captain be off the field, another player can be nominated to take his place. Each team is allowed one unsuccessful challenge per game;

putting a sensor in the ball and under the area of the try line and sidelines would help in knowing whether the ball not only went on and over the line but also the amount of pressure that was put over it. Then a value should be placed and set as threshold of pressure that must be placed on the ball in order for there to be "pressure on the ball" when awarding a try

The smart ball uses radio-frequency identification (RFID) technology to alert referees to the likes of forward passes and offside incidents. 'The high-precision RFID tracking we use is accurate to the nearest centimetre, and is embedded in the ball and in devices worn by players,' explained Sportable CEO Dugald Macdonald. 'We then superimpose a virtual 3D grid on the field so that the devices recognise when the ball has gone over a certain height or when it has moved forward relative to the ball-carrier.' The alerts reach officials in less than half a second, allowing referees to check decisions with minimal interference to the game.

Shinty
In shinty, the Camanachd Association allows the referee to request the opinion of a video umpire if there was or wasn't a goal (offside or foul leading up to the goal) or if it was or wasn't a penalty. The team is also allowed to call for a review known as a "team referral" by each team captain, to query a goal or penalty decision, a team has 1 referral throughout the match.

Tennis
FOXTENNuses 40 HD high speed cameras (2.500 fps) with 10 high-speed lasers to automatically detect where a ball has landed on the court. There's no risk of system occlusion. Precision is also guaranteed by the positions of the cameras at the end of the court lines, at ground level, in order to be able to see exactly how the ball bounces as close as possible. Being able to see the ball from the ground allows the system to notice the actual contact of ball's lower curve and the real contact mark on the surface. For any ball that landed on the baseline and service line a bird's eye camera view is used, using Hawkeye, for sidelines and center service line normal FOXTENN camera is used