The protagonists being forced to fight in a gladiatorial arena or fighting pit is littered throughout sci-fi and fantasy mediums. (Star Wars, Star Trek, Planet Hulk, Game of Thrones, John Carter, Mad Max, Hunger Games). It is also a staple of roleplaying games. It is an interesting way to start a campaign(DCC funnel anyone) or a great place to introduce new players into your game.
The players are forced to fight for spectators in an arena. This could be a grand coliseum or a fighting pit. How they got in this situation is up to you. It could be the result of them being captured or part of a bargain with the authorities of the place or even something they volunteered as a show of skill or as part of a contest.
The mood of this Set Piece depends a lot on the scene before the big fight. This should be a scene where the gladiators sit in a room waiting for the fight to begin. If it is the standard gladiatorial fight, then this scene should be littered with NPC combatants as well. If the players don’t step up to lead the rabble, feel free to have an experienced NPC combatant do so instead. Or have one oppose what the PC’s are playing. Have other NPCs ask probing questions. These people are probably expecting to die so they are looking for some hope in the PC. The scene before the fight sets the tone and is a great chance for RP.
The Gladiatorial fight itself should be hectic and brutal. Keep the combat fast describe the immediate threats for combat characters but the big picture for those hanging back.
This is where you can have fun. What are they fighting? Monsters brought in from exotic lands? Other intelligent creatures put in the same situation? The threat can be overwhelming or it can be manageable, but the obvious threat shouldn’t be the only one. Trap doors containing other creatures, spiked pads, whirling blades, rising platforms, all can be great threats. If it is a big arena don’t let it be a standard flat surface to fight on for long. Have some surprises up your sleeve. Make sure you show the NPC and other combatants falling victim to these things as well.
The other threat is their captors. Are they trying to escape? Is there an opportunity here?
Combat is heavy in this Set Piece, but make sure you give things for your non-combat characters to do. Allow them to study opponents point out weaknesses. Inspire the NPCs, rescue the NPCs, warn the NPCs. disable/override the traps/mechanisms. Make sure there are options.
Don’t worry about the mechanics for every NPC if there are many. Describe them fighting and dying. Only really roll the dice on ones the PC took a shine to in the pre-fight scene.
Include NPCs. Give a few NPCs personalities and put them in interesting situations. Maybe the veteran fighter is a real jerk but a great fighter, will the bard call out to him when he notices the spiked trap the veteran is about to back into?
Make it a spectacle. Have a Master of Ceremonies, and a large crowd. Describe the crowd and their reactions to the action on the pitch. They are as much a character as the PCs in this scene.
When the shit hits the fan let it. Sooner or later the fighter is going to pry open that trap door and use it to try to escape. Or some other concoction. What the players do is out of your hand, improvise the best you can, but don’t have a fast response from the enemy. It’s public spectacle and if the king quickly calls for his guards then the populous will know he doesn’t have everything in his power.
If the players don’t seem to be trying anything but fighting then let the fight come to a natural end. Don’t drag it out. Maybe they plan on escaping that night.
If a player goes down… I think this would be an acceptable time to finish them. Gladiatorial fights are brutal. It would be a good death for a PC.
Have the traps make the fighting interesting in narration but don’t require a roll every time. “You block the big Northlanders overhead ax swing with your stave. He puts his weight into determined to overpower you. However spikes quickly shoot up from the floor in between you forcing you both back in opposite directions. ”
Make the traps separate the party. One big group watching each other’s back is sound tactics, so pick a few off from the heard.