On Monday, the United States was eliminated from the Copa América in the group stage after losing a must-win game 1-0 to Uruguay.

The goal was a hugely controversial moment, with fans and pundits adamant that the scorer, Mathías Olivera, was clearly in front of the last defender when the ball was last touched by a teammate.

So, why was the goal allowed to stand by the VAR?

United States 0-1 Uruguay

Possible offside: Olivera when scoring

What happened: The only goal of the game came in the 66th minute when U.S. goalkeeper Matt Turner failed to hold a header from Ronald Araújo, and Olivera pounced to score on the rebound. The U.S. appealed for offside against Olivera, and a lengthy VAR check followed.

VAR decision: Goal stands.

VAR review: At the Copa América. there’s no semiautomated offside technology (SAOT). The video assistants have the legacy version, which uses crosshairs and requires the manual application of the lines to the two players, or to the attacker and the ball.

From one camera angle Olivera looked to be clearly offside, while the other used by the VAR looked closer but still offside.

One of the biggest misconceptions of the crosshair technology, which is also still being used in most domestic leagues, is that the VAR has used the “wrong angle.” Yet the whole reason for using it is to fix the parallax error — which causes displacement in the position of objects (in this case players) due to the viewing angle. The technology is mapped to each pitch, taking into account any camber, to ensure it is as accurate as possible.

Being unable to clearly show why an onside or offside decision has been reached has been a major issue with crosshair technology. We’re left to look at the camera provided by the television coverage, which can often be misleading — and when the lines are placed there’s little confidence in the outcome. It’s why a player can look offside — or indeed onside — to the human eye, yet the VAR can produce a different result.

For the Olivera decision, there’s more to it. Because this software has inconsistencies, both in terms of when the ball has been touched by a teammate and the plotting, players are given as onside if the two lines are touching. In other words, they are level — in the spirit of the wording of the offside law.

If a player is onside or offside, a red line is displayed for the attacker, and a blue line for the defender.

If the two lines touch, only a single blue line is displayed — which indicated that, in the application of this technology, Olivera was level with USMNT defender Chris Richards. Olivera may well be very marginally offside, but the benefit of the doubt means he’s given onside.

The video released by CONMEBOL on Tuesday showed the VAR determine the touch point by Araújo using multiple angles, then place the offside line to the foot of Richards.

Before the vertical crosshair line is moved onto Olivera, the red attacker line is present.

But when it is moved onto the knee of Olivera (you can see the change of position of the crosshair in the zoom in the top-right corner of the screen) it automatically disappears because the lines begin to touch.

This method was first used by UEFA several seasons ago, though European football’s governing body has recently moved to SAOT for its major competitions. Other confederations and associations using crosshairs followed suit, giving that benefit of the doubt to the attacker.

With SAOT, an animation takes viewers in line with the decision and shows exactly which part(s) of the attacker is offside, or how a defender is playing them onside.

The flip side is that SAOT is more accurate, so the benefit of the doubt — or lines touching — is removed.

On Saturday at Euro 2024, Denmark had a goal disallowed against Germany when the toes of Thomas Delaney were ahead of the last defender. With crosshair technology, the benefit of the doubt would have ensured the goal wasn’t ruled out.

Similarly, if the Copa América had upgraded to SAOT, there’s a high probability that the Olivera goal would have been given offside — because goals are ruled out to a far smaller margin.