I think that example is one those that once the investigation is in place that very few of you responses to subdue the guy is going to be unacceptable. Excessive force has to be completely disproportional to the problem at hand.The biggest skill a cop needs in communication, verbal and listening. You don't need to be a hard man you need to be both robust and compassionate.
People also never seem to take into account Police Officers are still just people. You can have all the training in the world to deal with specific situations. Yet when your on your 7th straight night, you've finished late four shifts on the trot, you've a new born child, you and your partner are worrying over money. Yet here you are 3 in the morning and some tw@t in Rushden has decided to pull a knife on you and a colleague. Your nearest back up is ten minutes away.
You've got to make the right decision. What use of force is acceptable, get in wrong you might end up suspended and in court yourself.
Welcome to the modern world of policing.
Still you break a guys arm and yeah it has to be investigated that is part of holding police to account. It might of been fine but you can't give those of authority carte blanche to do what they like. Otherwise it will get led to abuse.