http://kenpom.com/blog/index.php/weblog/entry/why_i_dont_believe_in_clutchness

"Whoa, Nate, what’s up? You appear to be mentally weak, unable to make free throws with the game on the line, and probably unable to carry out basic day-to-day tasks as well. Then again, what explains the fact that Wolters is so bad in the last five minutes but nearly automatic in the previous five minutes? He could carry the gene for Wroten Pressure Threshold Disease, or it could be that clutchness is crap. I vote for the latter*.".....

"*To be clear, I do believe that players generally perform better when the outcome of the game is in doubt than when it’s not. And if you want to call that clutchness, I’m fine with it. However, it’s a small factor in a sea of dozens of other factors that influences a player’s performance in any given possession. I don’t believe that a handful of special players have super-duper clutch powers."