Yes, in fact. His hit stunned her, preventing her from flopping around any further and possibly falling out of the hold of the other officers onto the concrete (which might have resulted in her cracking her head on the pavement).

She smacked the piss out of him, he had every right to put her to sleep, why does the cop deserve to be backhanded hard enough for it to be audible

Did I miss the part of the video where they shot her a bunch of times?