Maybe you could think about it like this: all major leaguers are clutch. To stay in the bigs, it takes an insane amount of talent, and an insane amount of concentration. Hitting major league pitching is just really hard. Everyone knows that. If you can concentrate any more, you will use that. And if you want to talk about stressful, I expect a rookie season in the bigs would be at the top of the list. Not the playoffs when you are 31 and an established player. However, part of the reason that some people wash out, might be mental. They are prone to lapses in concentration, or their game lowers under stress. If you care about the game and making a career out of it. If you have that self-interest to set yourself and your family up financially, then all of the at-bats are going to be big until that happens. I'd usually assume this kind of thing is a matter of talent, but whatever, sometimes there's a grey area on what's what exactly. This is just another one of those things were the level of play is so elite that you are going to have weird findings. Like DiPS or catcher ERA. Stuff that people don't want to believe, but it's true because you have to have so much of whatever that "stuff" is or you never get your cup of coffee. I can fully agree with that, but none of it takes into account situational hitting, and I would argue people who use the term "choke" only use it in refernce to situational hitting. Nobody says a player "chokes" when he stirkes out to make the first out of the top of the second inning.