No, it is not a performance measure. It is an attribute. The hitter can't control what happens after he hits the ball and the pitcher can't control what happens after he releases the ball. The clutch player is calm under pressure and can perform optimally. His abilities don't increase in a clutch situation. He is just able to perform up to his abilities without adverse effect. Often this will translate into statistical success, but frequently it does not, because there are intervening factors including opponents who may also be clutch. It can't be measured, because it is an attribute. How do you identify clutch. The other players and coaches can usually tell. It can be in another player's eyes, his bearing and other ways. Similarly the frightened choking player will also exhibit tells. Clutch is an attribute. Some have it. Some don't. Good players are not necessarily clutch players, and mediocre players can be clutch. A player can be clutch until he faces another player who is better and more clutch. A clutch player is not always clutch. He may have choked at some points in his career. As in golf, everyone chokes at some point. The guys who choke less than the others are the great ones. Ortiz was predominantly clutch. Denying that clutch exists, because it cannot be proved statistically is just foolishness -- a point about which to make a fatuous argument and act like a smarty pants.