Under the current laws of the game, if the ball touches a defender before reaching an offside player, that player is not offside. However, the decision ultimately lies with the match officials on the day and in this case, the goal was disallowed.
Overall, it was a thrilling encounter between two top teams in the FA Cup, with Manchester United ultimately coming out on top in the penalty shoot-out. The result will surely boost their confidence as they prepare to face Leicester in the next round. Arsenal, on the other hand, will need to regroup quickly as they face Tottenham in a crucial Premier League clash.
But their resilience in this FA Cup tie, despite being down to 10 men for much of the game, will give them hope ahead of the second leg at Old Trafford. Arsenal will feel they should have put the tie to bed, but the missed chances could come back to haunt them.