[Update]: I just read an excerpt from Bielock's book; she mentions to New Yorker piece (written, it turns out, by Malcolm Gladwell), but rejects the distinction between panicking and choking. She also offers a definition of choking:
Choking under pressure is poor performance that occurs in response to the perceived stress of a situation. Choking is not simply poor performance, however. Choking is suboptimal performance. It's when you—or an individual athlete, actor, musician, or student—perform worse than expected given what you are capable of doing, and worse than what you have done in the past. This less-than-optimal performance doesn't merely reflect a random fluctuation in skill level—we all have performance ups and downs. This choke occurs in response to a highly stressful situation.
I know Mike is a Sox fan, but I have to let Buckner off the hook as an all-time choke. That was an error. But Buckner was a bad fielder who could not walk and should not have been in the game at that point. The definition above further exonerates Buckner--I am not sure that error was so suboptimal for him. If anything, the bigger choke was by the Sox relievers in the eleven pitches leading up to Buckner's error.
Choking to me requires someone falling from heights and it typically is more than one single play. I would point to Jana Novotna's meltdown in the Wimbledon Women's Final in 1993 or Greg Norman at the 1996 Master's--on the verge of prevailing, their entire games fell apart over a series of plays.