Referee Got It Wrong
Andy Gray was the commentator at that match. He said that 100 times out of 100 if it had happened outside of the box it would have been given as a foul = free kick. If it`s a foul out of the box then it`s a penalty inside the box. Simple as that. Even Jamie Rednapp, son of the Portsmouth manager, Harry, said he thought it was a clear cut penalty. Jamie Rednapp was in the studio alongside Brian Robson, who thought the same thing.
Now, if United had converted the penalty, they would have led by 1-0. Portsmouth would have had to have come out on the attack, opening up ther defence, and United would probably have scored more goals, or at least kept their lead, thus resulting in a victory.