Having been fouled, and lying on the floor, van Persie had the ball smacked off the back of his head by Ashley Williams, leading to an on-field brawl.
Williams has claimed he was trying to clear the ball, but the whistle had been blown at least a second beforehand, which may not seem like much, but is definitely enough time for a professional footballer to decide not to kick the ball. Sir Alex dramatised the incident after the game stating “Robin van Persie is lucky to be alive. It was a disgraceful act from their player, he should be banned by the FA. Robin could have had a broken neck.” which is a frankly ridiculous summation of events and, in true Sir Alex style, is clearly designed to detract attention away from the final score.