I didn't like how captured raiders and gunners use ranged weapons in arena matches. So I replaced their guns with melee weapons like baseball bats, iron pipes etc. They will now fight each other in a more gladiatorial style.

I also added three new types of fighters, they all spawn with melee weapons:
* Synths
* Scavengers (look like settlers, pretty much normal wastelanders stuck in a cage, good for a raider playthrough I guess)
* Raiders (these guys are hostile towards other raiders, which means you can have raider vs raider battles)

All cages appear under the cages tab in the workshop. (Wasteland workshop DLC required)
I might add some more cages in the near future.

I recommend using some items from the Homemaker Expanded mod to build your arena.
Specifically the HOMEMAKER > FENCES > CONCRETE WALLS - Retaining window.
They are bulletproof windows which will stop your settlers from trying to attack the combatants and vice versa.