A running back (RB) is the position of a player on an American or Canadian football team who usually lines up in the offensive backfield. The primary roles of a running back are to receive handoffs from the quarterback for a rushing play, to catch passes from out of the backfield, and to block.

There are usually one or two running backs on the field for a given play, depending on the offensive formation. A running back may be a halfback (HB for short, in certain conexts also referred to as a tailback) or a fullback (FB). While a fullback is technically a running back, in modern parlance the terms "running back" and "RB" are frequently used to refer only to halfbacks/tailbacks.