There was great controversy in Manchester City's win over Aston Villa on Wednesday evening.
The game was locked at 0-0 going into the final 15 minutes.
Pep Guardiola's side took the lead in disputable circumstances through Bernardo Silva.
Rodri appeared to be in an offside position when he dispossessed Tyrone Mings inside the Villa half.
The Spaniard passed the ball to Bernardo Silva, who then produced a wonderful finish to break the deadlock.
Villa were left fuming.
Dean Smith took his protestations too far as he was shown a red card on the sidelines.
But why was the goal allowed to stand?
Peter Walton, speaking on BT Sport, explained the decision after the game.
"The law says a player in an offside position receiving the ball from an opponent, who deliberately plays the ball, is not considered to have gained an advantage," he said.
"So therefore, Mings playing the ball deliberately, plays the Man City player onside, even though he is in an offside position. Therefore, the goal should stand and he wasn't gaining an advantage from where he was.
"That's the law. The fact that Mings makes a deliberate play on the ball negates the fact that the player was in an offside position. Because it was a deliberate player on the ball it's a good goal."
Mings saw Walton's explanation and he wasn't happy as his vented his frustrations on Twitter.
"Never even heard of that rule, just let players stand offside, then run back & tackle you? In hindsight I should’ve cleared it, 100%, but didn’t even know that was the case. Nonsense", he wrote.
Grealish also spoke out after the controversy.
He wrote: "A bit confused with that offside rule if I’m honest but beaten by a brilliant team. Rest up and then back at it Saturday."
It's a shame that the game was decided by that goal.
Villa gave a great account of themselves and to lose in that fashion must have been hard to take.
By law, the goal should have stood, but it's definitely one that the rule makers should look to change in the future.