The guy that referreed the Italy/South Korea game in WC02 was one of the worst officiated games I can recall. He was later suspended by FIFA or his federation for sucking so badly. Took away (wrongly) a golden goal for Italy then gave Totti a yellow (his second, so a red) for diving in the box when he was fouled.
Totti's red is at 1:30 with the disallowed golden goal just after it. Spain were also robbed when they played South Korea, highlights are after the Italy highlights, had a goal wrongly disallowed in like the 88th minute that would have won the game for them.
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Peter Vink (reffing in Euro now) blew an obvious penalty for Arsenal in the first of their two Champions League ties with Liverpool this year.
I don't know how much of it is incompetency and how much is just the difficulty in officiating soccer, but officiating is generally horrendous in soccer. It is physiologically impossible to watch a ball being kicked and a defensive line at the same time (an offside) yet they continuously refuse to add replay to the game.
Webb is actually a very good official.