We're all getting our knickers crossed a little here. The Captain will very rarely get involved. It's not their domain, most will simply expect the cabin crew to deal with it..... And the majority of cabin crew will have no problem with dealing with it. If it became particularly abusive or violent and this was whilst on stand then the Captain, or indeed FO, would likely get involved.... But only for the protection of his/her crew. That scenario is still pretty rare though and it is important to add that no flight crew will get involved in disputes, violent or other whilst the aircraft is in the air. At most carriers this is simply not allowed.