Wiktionary
center field
n. 1 (context baseball English) The part of a baseball field which is beyond the infield and straight ahead left if you stand on home plate and face the pitcher. 2 (context baseball English) The defensive position in the outfield in the middle, typically played by a player that can run fast. 3 (context idiomatic English) A central role in some activity that requires speed.
WordNet
center field
n. the piece of ground in the outfield directly ahead of the catcher; "he hit the ball to deep center" [syn: center]
the fielding position of the player on a baseball team who is expected to field balls in the central third of the outfield