How big of a sample size is big enough for a batting average in MLB?

[Karak567]

Usually they show "this guy is .333 against this pitcher, 3 for 9 lifetime" and I think to myself "well that sample size isn't nearly large enough."

We do a lot of discussion about sample size in poker, but what at-bat sample size in baseball is big enough to draw conclusions about a hitter or a pitcher/hitter match-up?

20? 30? 10? 50?

[Jack of Arcades]

We already had this discussion, and you'll never really come to a conclusion because it's a lot more than 50. Now, on the other hand, watching them it'll take less than the stats.