[Adam]

most games, you're right. But if you know they're trash talking, you have the right to step in and stop it; even if it's mumbling. Simply tell them and the coaches you know what's going on and that you're not going to tolerate it. By you're own admission, you didn't manage this game well. Maybe this game would have devolved no matter what, and there's no way it could have been managed well. If it's obvious to you that these kids aren't complimenting each other under their breath, make the call.
You have no way of judging the OPs game and whether or not he missed signs. Just because you didn't deal with the signs in your game doesn't mean he missed some in his. Sometimes, this stuff happens with no warning at all.