IMO, anyone who doesn't crumble (perform significantly worse than norm) under pressure is clutch. That's my definition. Taking that to be true, most players are clutch. Most players can perform to their normal abilities in higher leverage situations. There are some who will perform better than their norms in these situations, and whether that's a pure anomaly/coincidence or there's a real reason for it is up for debate. That said, I think it's quite a bit of a reach to say that players will step it up another notch in key spots. It's hard enough as it is to hit a baseball, I don't see how the gravity of a certain situation can increase a player's ability to perform. But, anyway, most players are clutch. The only ones who aren't are the un-clutch gutless choking dogs. Then again, there's stuff like adrenaline and stuff that kicks in for people and some people actually do rise to the occasion in important moments (just generally, in life), so who the hell knows. I think it's just easier to look at it my way.