Clutch and choke do exist in small sample sizes. It is questionable if they are inherent qualities of athletes.
We can't label anything clutch or choke without actual game results. A player sitting on the bench in a high pressure moment does not possess a quality of clutch or choke. The evidence of clutch and choke is not what we think is in a players heart, but what actually happens on the field.
There is the argument about a player possessing clutch as a distinct skill. The numbers suggest that since it is not repeatable with any statistical significance, it is not a skill. Unlike say, hitting HR's, which can be repeated with statistical significance. So even though Jacoby Ellsbury hit 32 HR's in 2011, his career HR frequency of 1.9%, which is below the MLB avg. of 2.7%, would strongly suggest he is not a HR hitter as part of his skill set. David Ortiz, on the other hand, hit HR's 5.4% of the time, double the MLB avg. His skill set does include hitting HR's.