Football may be the biggest game across the world, but it has taken its time in catching up with other sports when it comes to adopting video technology.
But the Video Assistant Referee (VAR) system -- which debuted at the top level back in December in the FIFA Club World Cup semifinal between Atletico Nacional and Kashima Antlers -- was implemented in another high-profile match on Tuesday during Spain's 2-0 friendly win in France.
While the introduction of VAR has been broadly welcomed across the sport, there have been complaints about the amount of time reaching a decision takes, causing a long pause in matches and stifling celebrations for players and fans alike.
A variety of video referral and appeal systems have been used in several other sports for years -- notably rugby union, cricket, tennis and in the NFL. So what, if anything, could football learn from these other sports in its own implementation of video technology?
We asked ESPN's experts for their take on the positives and pitfalls in their respective sports.
The role of the Television Match Official (TMO) is a constant battle between perfection and distortion, as administrator Edward Griffiths put it, and it continues to be a polarising aspect of the game. The TMO's powers now extend not just to clarification over whether a try has been scored or not, but also to any potential infringements in the run-up to a score, and to possible foul play.
It risks matches becoming stop-start affairs in a sport which already struggles with scrum sequences sometimes taking an age. The TMO and its increasing omnipotence also leads to a school of thought that referees are being undermined.
The role of the TMO was thrust into the rugby consciousness during the 2015 Rugby World Cup where a total of 132 decisions were sent upstairs. Matches went on longer than the usual timeframe, and play was disjointed.
But it has become a key part of the game. Rarely is the legitimacy of a try disputed post-TMO and it has led to more foul play being penalised mid-game rather than one for postmatch citings.
It is not the finished article; the slow-motion replays afforded to the referees distort high-paced, mistimed tackles and causes general frustration. The fact that referees can award a try, but then catch a glimpse of a replay on one of the stadium's screens and call for a review is also flawed. The TMO is here to stay but will inevitably undergo continual reviews and redefinitions of its powers. -- Tom Hamilton, ESPN Scrum
Broadly speaking, yes, video technology has been A Good Thing for cricket. But how long have we got to debate the finer details?
These days, in most of the sport's marquee tournaments (when it is worth making all of the relevant tools available to the TV umpire) technology has succeeded in eliminating howlers -- in particular, line decisions such as run-outs and stumpings, when the question of "in" or "out" is a simple binary issue of whether the ball has hit the stumps before the bat has crossed the line. No one can quibble with the benefits of such clarity.
The more complex issues, however, arise on those regular occasions when decisions have to be reached from incomplete information -- most fundamentally, lbw (leg before wicket) appeals, which in all too many cases are still debatable even after the verdict has been reached.
Essentially, the naked eye of the on-field umpire has been replaced with the hawk-eye of ball-tracking software, but that is merely substituting one form of absolute authority for another. There still has to be an arbitrary tipping point between "out" and "not out" (and the International Cricket Council has debated at length where that point should be). Either way, if a batsman is dismissed or reprieved by 0.01 percent of a seam's width, or the slenderest of "snickometer" scratches, neither side is going to be 100 percent convinced by the verdict.
And we haven't even addressed the issue of "foreshortening" for disputed catches, when the process of projecting a 3D live event onto a 2D replay screen cranks open a brand new can of worms... -- Andrew Miller, ESPN Cricinfo
More than a decade later, Hawkeye technology has eliminated almost all uncertainty in shots close to the baseline. The video replay system is fast and efficient, and allows players to challenge certain calls without getting angry with line judges or chair umpires.
It means that the combustible John McEnroe, Illie Nastase and Jimmy Connors would have little ammunition to yell at any of the authorities for a call they disputed.
In today's game, we see few incidents when it comes to line-calling conflicts. Of course, not every court is equipped with Hawkeye, but more and more facilities are implanting the technology.
But this technology goes beyond line-calling. Hawkeye technology has been innovative in its ability to track ball trajectory and speed. Players can now track their games with more tangible feedback.
Tennis was late to the game in introducing video technology, but it seems everyone has benefited, whether on the practice court or in the heat of competition.
The NFL's replay review system unquestionably helps referees officiate games more accurately. In fact, the biggest criticism most fans have of it is its limited scope. Coaches can challenge decisions from a relatively small menu as defined in the NFL rule book.
The intent is to review objective calls: whether a catch was made, for example, or if a player was in or out of bounds. Referees, however, have the final say over subjective penalties such as pass interference or holding.
The idea is to correct objective calls when technology shows a clear and obvious mistake. In 2016, 345 plays were either challenged by coaches or reviewed by the replay official on site. Just over 43 percent were reversed. So that means the system saved the NFL from making 149 mistakes that could have impacted the outcome of games.
The league further refined the system this spring to centralize review decisions in its New York offices. This will allow for shorter stoppages in play and more consistent decisions across the board.
The system is far from perfect, and many games are still impacted by mistakes that cannot be reviewed by rule. But it is difficult to imagine the NFL without it, which is a testament to its important role in game administration. -- Kevin Seifert