sixth man

plural sixth men

1. ball gamesA player who is not a starter but comes off the bench much more often than other reserves.
2. By extension, a person or group who is not part of a team, but who supports or contributes to the success of the team.

   Our sixth man, the Williams Arena crowd, was into the game, all 15,491 of them.

   1997, Clem Haskins, Marc Ryan, Clem Haskins: Breaking Barriers, page 143