1. To intentionally reveal damaging or unflattering information about another's character or transpired event, while at the same time trying to make themselves look good or innocent in the eyes of the listener. To shift blame or attention in a cowardly way.
The varsity quarteback was thrown under the bus by a sophomore when the coach was told who toilet papered his house.
In sports usage: A player that is always pissed off. Usually said off an outstanding player when anything short of perfection isn't good enough. If Randy Johnson gets a win, he should have struck out 15, or have thrown a shut-out, or a no hitter. Basically a red ass is never pleased with his or his teammates performance on most occasions.
Player A: What's eating him, he just went 3 for 4 and we're only a game out of first?
Player B: He's such a red ass that even if he went 5 for 5 and we were 10 games in first he still wouldn't crack a smile.