In arena football, a specialist was a player, other than a quarterback or placekicker, who was exempt from the league's one-platoon system ("Iron Man"). Under the original Arena football system, six of the eight players on each team were required to play both offense and defense.^[1]

One of the two offensive positions was required to be a quarterback or, in the event of a kick, a placekicker. The other was known as an offensive specialist (OS). Offensive specialists usually played wide receiver, either as a flanker or a slotback. The defense was allowed two defensive specialists (DS), who almost universally played in the secondary. Players were referred to as "specialists" instead of their more traditional positional designations (example, a player would be called a defensive specialist and be designated as "DS" on a position chart, instead of a cornerback or CB).

Specialists were usually required to participate on special teams, a requirement that was not extended to quarterbacks.

The specialist designation was eliminated after both the Arena Football League and af2 abandoned the one-platoon system prior to the 2007 season. Most other indoor football leagues have used free substitution since their inception.