The worst thing turns out to be a referee who takes away a goal–a great goal, a game-deciding goal, an end-of-game goal–with no plausible explanation. Wait–forget "plausible." The referee in the U.S.-Slovenia game nullified the Americans' go-ahead goal with no explanation at all. It kind of makes you miss Jim Joyce, the umpire who blew a big call earlier this month but was man enough to admit it and cry about it, too.
But the really damaging part of the bad call at the Cup is the impression it leaves among Americans who aren't really soccer fans but were watching the game out of curiosity or some sort of patriotic fetish. Imagine them watching Friday morning's contest and seeing it so arbitrarily and so wrongly decided, based on what looks like the referee's whim. Why would they come back to watch again?