"Gunfight at the O.K. Corral" role (4)
I believe the answer is:
earp
(Other definitions for earp that I've seen before include "Wyatt --, Tombstone lawman" , "See 4 Across" , "Wyatt - (O.K. Corral)" , "Wyatt -, renowned US lawman" , "Wyatt --, US law officer" .)