Just finished my first playthrough the other day and just came across the combat zone, is there a way to compete in the combat zone?

I know in previous games you could become a boxer etc...

Nope. Not at this moment. But people have plans for mods already. Time will tell if they succeed.

Every time I go there, I end up having to fight everyone other than Cait and Tommy. Was that supposed to be an arena place where we watch fights?

Missed opportunity for sure.

I wondered this same thing, but no matter what I did those raiders were going to be hostile so I launched a mini nuke and sent what's her face to the castle. Definitely a wasted opportunity.

I remember seeing a short clip of the combat zone in one of the early trailers for F4, giving the impression we could at some point be in the area taking part. A little disappointing with the actual outcome.

I think I had a bug in the combat zone, since Cait wasn't in the ring when I went there which made some of the dialogue weird since they were talking about a fight that hadn't happened.