The Union had an opportunity this past Saturday to join their Philadelphia sports brethren in one of the more ignominious chapters of the local history books: tales of being done wrong by a referee's video replay.

On the first official night of video replay in Major League Soccer, the first replay incident in league history took place at Talen Energy Stadium. With a little less than 12 minutes to go in the game, Union goalkeeper John McCarthy made a charging stop on FC Dallas' Cristian Colman, but offered a juicy rebound to Maximiliano Urruti, who promptly buried the ball in the net.

As McCarthy crumpled on the field injured, referee Ricardo Salazar told both teams to stop play for a moment. At first, that seemed to be so the medical staff could attend to McCarthy. But within seconds, Salazar made clear that it was for more than that. The play was being reviewed by the replay booth upstairs.

Television replays promptly showed that Colman had clearly kicked McCarthy in the groin. The replay booth saw the same footage, and relayed that perspective to Salazar. He listened for a few moments, then made the distinct rectangular motion to show he was going to look at a monitor on the sideline.

To the delight of the team and its fans – and perhaps to the surprise of the more grizzled souls in the crowd – Salazar overturned the goal.

It was a defining moment of the game for the Union, who went on to win the game comfortably. It was a defining moment for Major League Soccer. And it was arguably a defining moment for the global game, given how many leagues around the world were watching MLS become one of the first soccer leagues in the world to implement video replay in live games.

"For them to adopt this system shows that the league is progressive, and thinking about more than just the present," Union manager Jim Curtin said. "They're thinking about the future and where the game is moving."

Officially, the system is called VAR, short for Video Assistant Referee. That title refers to the person who sits in the replay operations room and makes the call to review a controversial moment.

The VAR is joined in the booth by an assistant referee who communicates with stadium officials and the television broadcast, a replay operator who oversees the intake of camera feeds, and an assistant on the field who stands next to the game referee's replay monitor.

The on-field video replay monitor used by the referee at the Major League Soccer Homegrown Game earlier this month at Toyota Park in Bridgeview, Ill.
Jonathan Tannenwald
The on-field video replay monitor used by the referee at the Major League Soccer Homegrown Game earlier this month at Toyota Park in Bridgeview, Ill.

The booth crew has access to every camera angle that's available to the television broadcast. There are no views exclusive to the VAR, nor are there views available to viewers at home that the VAR can't see. MLS mandates a minimum of eight camera angles at each game, above the global requirement of five. Most MLS games have many more cameras than that.

Although the VAR watches every moment of the game, only certain specific situations are subject to review: goals, penalty kicks, potential red cards, and mistaken identity in awarding a card. Any other calls, or non-calls, are left alone.

Most reviews will occur during stoppages of play. It's worth noting that if the ball goes out of bounds and play is restarted before a booth review can be concluded, the referee can't stop the action. That will cause some controversy.

But if action is paused, referees can bar players from restarting action – via throw-ins, for example – until the booth review is done. If that means blowing the whistle a few times, so be it. And a player who tries to show a referee up could get a yellow card for defiance.

If play has not stopped while the review is ongoing, the VAR can advise the field referee to make a review.

But no matter the circumstance, the VAR cannot officially overturn a call made by the referee on the field. He or she can advise, but only the central referee can make the ultimate decision.

MLS went to great lengths to prepare for the rollout of video replay. The league's first plans to implement the system were drawn up three years ago, and trialed in nearly 140 games at various levels over the last 18 months. The first efforts came in the lower-tier USL last year, and were followed by MLS preseason and youth team games this year. Then came unofficial tests in regular-season MLS games this year, and a soft launch in last week's Homegrown Game outside Chicago.

The league also has made a big push to educate fans and media about video replay. There are explanatory videos on the league's website, and there have been seminars in MLS markets across the country to give media a first-hand look at the technology.

The man in charge of those seminars, and of the rollout of video replay in MLS as a whole, is Howard Webb. A longtime referee in Europe, he gained worldwide renown for taking charge of the biggest games in the English Premier League, UEFA Champions League and the World Cup.

Part of that renown came from the intimidating personality Webb showed to the planet's biggest soccer stars. But in his video replay seminar, he was downright congenial.

"We feel it's going to be a useful additional tool for our officials to use to avoid making clear errors, or to deal with serious missed incidents," Webb said. "It's not going to change the way the game is played. If it does that, then it's not doing the job that it's meant to do."

Webb emphasized that the key question the VAR must ask while watching footage is not whether the initial call was right, but whether the call was clearly wrong.

"We're not here to change the way the game is played, and we're not here to re-referee the game, either," he said. "We are just trying to give our officials a better opportunity to avoid making clear errors, the kinds of errors that change results of games and can quickly be rectified on a video replay."

Webb was also quick to acknowledge that in a sport as free-flowing as soccer, it's impossible to get every little thing correct.

"The game is beautiful [and] we love it for what it is: it's fast-flowing, it has ebb and tempo and flow, and it's not a series of set pieces," he said. "We're not aiming for 100 percent accuracy. Things will still happen in the game which are subjective, things which people can form different opinions on."

Former English Premier League, UEFA Champions League and FIFA World Cup referee Howard Webb is overseeing Major League Soccer’s implementation of video replay.
Jonathan Tannenwald
Former English Premier League, UEFA Champions League and FIFA World Cup referee Howard Webb is overseeing Major League Soccer’s implementation of video replay.

The biggest question for many observers isn't whether calls will be gotten right. It's how long it will take decisions to be made.

In the overturned Dallas goal, the ball went in the net at the 78:05 mark on the clock. At 78:16, Salazar pointed to his ear to indicate he was hearing advice from the VAR. At 79:21, he made a rectangular gesture – the shape of a television screen – to signal he was going to the monitor. He then walked to that monitor, located at the same end of the field where the play had occurred.

At 80:09, Salazar blew his whistle and waved the goal off. And at 80:48, he blew his whistle again to restart play.

The whole sequence took 2 minutes, 43 seconds.

There is no set rule for how long replays should take, or even a desired standard at this point. But the average time taken for a review and decision during the trial period was 2:41, so the Union-Dallas scenario was in line.

So was a video review in Sunday's Portland Timbers-Los Angeles Galaxy game. A Galaxy goal was disallowed when replays showed that U.S. national-team regular Gyasi Zardes committed a handball as he trapped a ball that he went on to shoot. The full sequence took 2:35.

Time taken for a review is added to the stoppage time at the end of that half.

"Yes, it does take more time with video review, but we feel that it's a price worth paying to get to a decision that is not a clear error," Webb said. "The ideal is as quickly as possible without sacrificing accuracy."

Curtin had no problem with how the review process played out.

"It worked out in our favor this week, but it was the right call, and it was handled very quickly and efficiently," he said. "There was no time wasted, no real lull."

Officially, MLS is not the first entity in global soccer to use video replay. That honor was claimed by Australia's A-League in April. The system was also used at FIFA's Under-20 World Cup in May and June and the Confederations Cup in July.

But given the profile of the game in America, and the widespread use of video replay in other American sports, MLS offers a high-profile testing ground. So far, much of the MLS community is happy to have it.

That includes, crucially, the referees themselves.

"For two years now, we've been training for this, and everybody is on board," Salazar told the Inquirer and Daily News a few days before coming to Chester for the Union-Dallas game. "It's going to change the game to something that we are not currently used to, and it's going to take not just the people in North America to grasp it, it's going to take people worldwide to give it time [and] to understand it. Once they give it a chance, I think it's going to be here to stay."

The video replay console at Toyota Park in Bridgeview, Ill., home of the Chicago Fire.
Jonathan Tannenwald
The video replay console at Toyota Park in Bridgeview, Ill., home of the Chicago Fire.

Of course, there are critics, and there probably always will be. Among the most prominent is U.S. national-team and Toronto FC captain Michael Bradley, who told the Toronto Sun that VAR is "not something that I'm a fan of at the moment."

Down the road in Montreal, Impact captain Patrice Bernier gave video replay a strong endorsement.

"I think we need it," said Bernier, who will lead his team against the Union this Saturday in Chester (8 p.m., CSN). "Every sport has [replay] assistance. I think it's going to be beneficial, and help out the games, the referees and the league.

If the VAR system continues to be a success in MLS, that might help other leagues worldwide embrace it. Germany's Bundesliga and Italy's Serie A will bring video replay to the world's elite in their coming seasons, and FIFA will use it at next year's World Cup in Russia. By that time, the technology should be ready for the biggest stage of all.

What-if scenarios for video replays

Most times, a replay call will be straightforward. A collision resulted in a foul or a dive. A foul was inside the 18-yard box or it wasn't. A goal scored was offside, or a waved-off goal should have stood.

But there are some situations where the outcome isn't so simple. Here are some examples of what video replay can lead to – and one important scenario where it can't be used at all.

1. A foul is called outside the box and a red card is given, but replay shows the defender actually got the ball cleanly, and should not have been sent off. The referee overturns the card and the foul. The result of the decision is a restart with a dropped ball, leading to open play.

2. A shot hits the crossbar or the post and comes down outside of the net, but is ruled a goal. Video replay shows clearly that there was no goal, as the entire ball must cross the entire line. (This is a situation where it really matters that the default presumption is the referee's call stands.) The result of the decision is a dropped ball on the six-yard line in proximity to where the ball came down – and in all likelihood, a mad scramble by the teams.

3. A player from the attacking team plays the ball forward to a teammate who is wrongly flagged as offside. Play is stopped as a result. This cannot be reviewed. The only times when offside calls can be reviewed are when the ball is in the net, which makes the play an official goal-scoring opportunity. If there is no shot attempt taken in the play – even if the offside player was headed for a one-on-one breakaway with the goalkeeper – the play cannot be reviewed.