Old English benc "long seat," from Proto-Germanic *bankiz "bank of earth," perhaps here "man-made earthwork," later "bench, table" (cf. Old Frisian bank "bench," Old Norse bekkr, Danish bænk, Middle Dutch banc, Old High German banch), from PIE root *bheg- "to break." Used for "office of a judge" since late 13c. Sporting sense "reserve of players" (in baseball, North American football, etc.) is by 1909, from literal sense of place where players sit when not in action (by 1889).
"to take out of the game," 1902, from bench (n.) in the sporting sense. Related: Benched; benching. Old English also had a verb form, but it meant "to make benches."