If this guy had been struck in the leg once or twice on the way to the driver's side door of the vehicle, he would have fallen to the ground; they could have cuffed him there.
This was SOP for, well, a couple of centuries. As has been pointed out, the Rodney King affair basically led to the retirement of the baton.
They just never replaced it with something equally reliable, so instead of striking a guy and knocking him to the ground, the cop has to shoot him instead.