Fight between PCs

Hello Everybody!
I have one simple question: What happen when two playing character fight each other? Let’s think about a duel challenge, with PCs facing each other with duel sword. How can I menage the fight with the Blade’s rules?
I know that BitD is structured to make player collaborate (they are part of the same band after all), but in a OneShot I wanted to make some change and cannot figure out how to solve this situation.
Has anyone ever been in this situation? Have you found solutions?
Thank you!

Have you looked at the section on PC vs PC on page 41?

It’s the same as the rules for PC vs. NPC action: action rolls, resistance rolls, fortune rolls; effects and consequences; and resolution into a new situation.

The section provides guidelines around ensuring the players are still collaborating, even if there characters fight.