I don't know the origins, but I'm guessing it comes out of the overly romanticized writings about the sport back in the day, when most fans couldn't watch the games, or even listen to them, instead they relied on a sportswriter to spin the tale. A guy who got a big hit at a big time would be considered clutch, or whatever similar word they used, while somebody who came up short was a choker. There wasn't much statistical analysis going on, instead they just wrote what sounded better. Explaining that a .300 hitter with a .400 OBP still makes an out 60% of the time, so it's not very reasonable to hate him for coming up short in a big moment wasn't nearly as interesting as saying some guy had all the skills but not the intestinal fortitude to get the hit when it mattered most. Is it possible then that there is such an attribute as choke (someone who's batting average or OBP or SLG goes down in important situations) but not really something like being clutch? I could see that an important situation could get a hitter out of their rhythm more than it could get one into it.