What Did He Think Would Happen Exactly?

In general, once you put hands on someone, and especially if that someone is a cop, things are likley not going to go how you want them.

The Detroit Free Press: DPD officer suspended for striking man in his 70s, investigation ongoing

Yes, the headline has the officer in trouble for hitting a 70-year-old, which, after all, sounds bad.

The 70-year-old was however acting the fool, not listening to officer commands to quit making a disturbance in public, and most importantly, hit the officer on his head first before the officer got physical with him.

The drunken 70-year-old thought he could take a cop, and he thought wrong. 

No description of the idiot beyond his age is given, for some reason.

So sure, the officer could potentially have chosen a lower force option than laying the drunk idiot out with one hit.  Then again, one could argue his action was a rather proportional response of a strike for a strike, and hard to call it unreasonable as it stopped the attack right there.  Had he tackled him or did other restraints it likely would have been the same use of force complaint and may have caused more damage.  Hard to see what further de-escalation the officer should have been done once idiot had his hands start flying like that - again all at the idiot's instigation. Indeed from the sequence of events reported, it seems the cop did act in a restrained manner with repeated requests for the idiot to stop his disturbance and leave the area, right up until the idiot decided to lay hands and hit him on the head.

Indeed, had Mr. idiot kept his hands to himself, the responsive strike would not have happened.

Personally, I'm of the opinion that if you go out and start stuff and strike a cop -- or indeed any member of the public -- and you're not acting in self-defense, you get what you get in return and shouldn't get to complain when you get hit back.