bench warmer
An athlete who does not get much playing time (usually because they are not very good or skilled). I'm just a bench warmer, so you won't see me out on the court much.
bench warmer
n. a ballplayer who spends most of the game on the bench waiting to play; a second-rate player. You’ll never be anything but a bench warmer.
benchwarmer
A person who is seldom or never active in an enterprise. Derived from the sports meaning of a player who rarely or never takes part in a game but is relegated to sitting on the bench, the term, which dates from the early 1900s, was almost immediately transferred to other circumstances. The sports meaning appeared in a 2006 film, The Benchwarmers, about three not very competent ballplayers.