Is there a fight system here?

Nope. You can make up one for your own use using dice rolls, but most of us just paragraph fight. You can set your own parameters for that (like how often a reply should be made or how many dodges) but the game itself has no rules for that sort of thing, except the standard "no powerplay, no godmode".

And there should always be an opportunity for a fight to be avoided, i.e. you and your fellow both should have the opportunity to pull your character out before a fight happens, unless of course they're trespassing, in the event they don't want to be forced into a fight. But that's not an official rule, it's just courtesy.