Although ground staff and Police are usually quite good at their jobs, if a passenger is to be removed the Captain should hold a two minute meeting with those involved to set expectations about how the removal will be conducted and set a clear expectation that another meeting will be held prior to using any form of physical coercion.
I imagine the Captain involved just assumed everyone would do their job in a professional manner and it didn't turn out that way.
I'll take a punt that the Captain was occupied doing the job that he is primarily employed for, pre-departure checks, maybe ground staff in the flight deck with LMC's to the loadsheet, minus 4 punters, plus 4 of god's gift plus 4 bags etc. etc. etc.
I'll take another punt that the punters selected to be kicked off were hand baggage only and didn't have any bags in the hold!