As far as I am aware getting involved in any altercation with pax is a complete no-no even on the ground. Disuption sufficient to require that means a call for Police to sort it out. Leaving the flight deck to deal with trouble in flight is, I have to say, almost beyond belief under any circumstances, and to hear of this being done post 11-9? Staggering! If the trouble is that serious it is a diversion matter, surely, and no one will question or criticise that? But I'd hate to be on the carpet to explain leaving the flight deck - and I don't think invoking "Captain's discretion to vary SOPs" would cut much ice in that case somehow.
No doubt the real facts will come out in the wash.