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Meaning of bench jockey

bench' jock"ey

Pronunciation: [key]
— Chiefly Baseball. Chiefly Baseball.
  1. a vociferous player, coach, or manager who makes a specialty of baiting or harassing the umpires or opposing players, usually from the bench.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.