Parva;
As a young P2 a P1 I was crewed with left the FD for a "comfort break" and was asked while out to help with a disruptive passenger. I ended up landing the aircraft alone as the P1 needed to go to hospital. Since then I've been very circumspect in involving FD crew in any form of cabin altercation.
An injured pilot is a major problem. I prefer a call from down the back, if its' really serious I'm happy to divert on the reccomendation of a senior CC member.
SND