When Liverpool and Norwich face off today in the season-opening match of the Premier League, fans in England may see a bit of tradition slip away. No longer will the referees act as the all-seeing, all-knowing gods of the pitch. They’ll have a team of second-guessers watching from above—the video assistant referee, or VAR. Despite major hiccups at the Women’s World Cup earlier this summer, and studies showing that the VAR system slows down the most beautiful game, the Premier League is set to finally institute video review. It is the last major soccer league to do so.

At nearly $6 billion in annual revenue, the Premier League is one of the world’s richest sports organizations, so the consequences to a team for a referee's penalty can be huge. Teams that lose and tumble in the standings get sent down to a lower-level league the following season. Playing in a lower league means less revenue for the team and the players. To try to get the calls right, Premier League officials spent two years figuring out how to make the video system work properly. Still, expect some weird stuff to happen on the field during this weekend’s matches.

"I have no doubt it will create some controversy because it is about the big decisions, but we are prepared for that,” interim league chief executive Richard Masters told the BBC.

The video assistant referee system, also known as VAR, adds a fifth official to the field along with a referee, an assistant referee, and two linesmen. That person—awkwardly also called the VAR—sits in a booth and monitors feeds from the multiple commercial broadcast cameras set up around the field to cover the match. If there's some doubt over a penalty, goal, or offsides call, the video assistant referee can review the play and then signal to the referee on the field to take a look at an image of the play on a screen on the sideline. After reviewing the play in real time or slow motion, the referee decides whether to change his decision. (At least in the Premier League, all referees are male.)

At least, that's how it's supposed to work. At the recent Women's World Cup, however, players and coaches were upset that the video system was being applied to minor infractions, such as the rarely enforced rule that goalkeepers must stay on their line during a penalty kick. Others complained that VAR should have been used when it wasn't, or that it didn't help referees make close calls.

While most VAR calls only take a minute or so on the field, some decisions have taken longer and slowed the pace and rhythm of a fast-moving and momentum-driven sport.

Two years ago, US referee Carlos Salazar had a pretty rough afternoon with VAR. He was the first Major League Soccer referee to use video review technology, during the second half of a match between FC Dallas and the Philadelphia Union on August 5, 2017.

“I made the first mistake,” says Salazar, a longtime MLS on-field referee who now works in the upstairs booth as a video assistant referee, about his initial call.

In the game, Salazar initially signaled a goal for Dallas forward Maxi Urruti. Then the video review began, but the technology didn't work seamlessly. The radio connection between Salazar and the VAR booth failed, so the crew had to communicate to a sideline official through a walkie-talkie, and then to Salazar on the field. After several minutes of back-and-forth discussion and after reviewing what happened on the field, he ended up overturning his decision. It turned out that Urruti had kicked the goalkeeper in the groin before striking the ball, a clear and obvious foul.