Eh...little excessive, IMHO. Throwing a punch, that quick, in the situation...he could've handled it differently. Pushed her away, restrained her better...he was alot bigger than her. If you can't restrain a 120lb woman, how you can be expected to wrestle a 240lb drug dealer, burglar, etc?
With obviously no secondary officer on scene, though, I'd probably have done the same thing and with as many men standing around me, as that officer had, I'd probably have drawn my sidearm, when they didn't step back...after he told them 10 times.
Not in a racist note, but it is the usual large group of black people...who, of course, are doing nothing wrong (said as sarcastically as possible)...then, when questioned by police, something happens and out come the video cameras and them yelling about racism.