The numbers guy at the WSJ examines the case of "clutch" hitting. A-Rod "lack of clutch" takes center stage.
Jahn Hakes and I looked pretty carefully for clutch effects several years ago. We were excited since newly available retrosheet data offered new ways of looking at the issue, including the "leverage" effects (changes in probability) of different hits at different times. We found nothing significant. Zip, zilch, nada. And we tried hard. We tried hard because I think real factors (psychological makeup, physical condition) have time-varying effects and thus contribute to some streaks. But randomness is so dominant in baseball that it apparently conjures up the bulk of them.