There's a mentality among pundits and fans that goes...you can't call that a penalty unless you're 100% sure. And my response to that is, why the hell not? A penalty AGAINST one team is a penalty FOR another team, and whichever way a ref misses a PK call, whether it's a false positive or a false negative, the effect on the game is the same. So if you're one of those people who thinks a PK needs to be 100%, you are basically OK with referees missing more calls than they should. When it comes to PKs, to me, the standard should be 51%. If you're 51% sure it's a PK, call it, because you'll get 51 calls right and 49 calls wrong, and that's+2 on the good side of the ledger.