warm the bench

Fig. [for a player] to remain out of play during a game—seated on a bench. John spent the whole game warming the bench. Mary never warms the bench. She plays from the beginning to the end.

Also, ride the bench. Be a secondary or substitute participant; wait one's turn to participate. For example, I can't wait till the head of accounting retires; I've been warming the bench for years . This expression comes from such sports as baseball and football, and their standard practice of having substitute players sit on a bench in case they are needed in a game. [Slang; early 1900s]