TCU coach Gary Patterson was planning to use backup quarterback Trevone Boykin as a tailback when the 15th-ranked Horned Frogs play Iowa State.
Boykin will be in the backfield Saturday, but instead as the starting quarterback with Casey Pachall (PAW-hall) suspended indefinitely. Pachall was arrested early Thursday on suspicion of driving while intoxicated.
The Frogs (4-0) were looking at Boykin as a tailback option since they've already lost their leading rusher to a season-ending knee injury and current starter Matthew Tucker is dealing with an ankle injury.
TCU, which has won 12 games in a row, is playing its first Big 12 home game.
Boykin is 9-of-10 passing for 74 yards and a touchdown, and has run 12 times for 122 yards and a score.