[mtn335]

I've officiated football, basketball, soccer, and softball, and played ice hockey; in my opinion, soccer is the most difficult of these to officiate. The demands placed on the one man or woman in the middle are much higher than in any other sport as far as number of players and amount of space in jurisdiction, and no sport has a higher-leverage decision than a penalty kick (an all but awarded goal, in a game where average games see fewer than three). Red cards are also brutal - playing short the remainder of the match - in terms of leverage.

The individual calls may not be the most difficult, but the overall demands are just brutal.

EDIT: I'm not a soccer referee right now (time, had to pick) but at the highest levels, the system just isn't working. I don't have a solution, but more eyes will, I think, be necessary eventually. And used more helpfully than AARs...