Referee Mike Dean had awarded a 53rd-minute goal after Raheem Sterling had run on to David Silva’s flick before putting the ball in the net.
But, following the introduction of VAR this season, David Coote, the VAR in Stockley Park, deemed Sterling to be offside when he received the ball.
Although the margin of offside was very fine, the technology proved that a part of Sterling’s body, that is not his arms, was just offside.
So Dean overturned the goal and awarded a free-kick to West Ham where the infringement took place.
Decisions such as offside are not subjective and are not part of the "clear and obvious" error element of VAR that was introduced in the Premier League this season.
Sterling was disappointed to have the goal ruled out but did not complain.
“It’s difficult during the game, but at the end of the day if the decision is right that's all that matters," he said.
Coincidentally, Sterling put the ball in the net 22 minutes later and again it was touch and go as to whether he was onside before scoring, but this time he was just the right side of the defender and the goal was allowed to stand after the VAR's check.
Coote was again called into action after Sergio Aguero’s penalty kick was saved.
Under the Premier League's VAR protocol, the VAR can intervene for encroachment by players that has a direct impact on the outcome of the kick.
Because Rice's encroachment fulfilled this criteria, the VAR recommended to Dean to have the penalty retaken and the City striker did not pass up the second chance, making it 4-0.
See: VAR at penalty kicks