Roar of the Crowd is a set of free rules for playing science fiction, fantasy or historical gladiator games.
gladiator
Spartacus Gladiator Rules
Andy Watkins has one page set of rules for games involving Roman gladiators. You can use the fine Wargames Foundry 28mm Gladiators to fill your arena.
Thumbs Up, Thumbs Down Gladiator Rules
Thumbs Up, Thumbs Down is a set of free wargames rules for gladiatorial combat. The rules are designed for up to ten players.