I've only just watched the video posted of the full context.
I saw the male cop slam the lad in blue's head against the metal machine during the start of the arrest (who knows why), which prompts the lad sat down to stand up and place his hand on that cop's right arm (like footballers do to refs). That male cop reacts and strikes first and the fight breaks out.
The lad in blue deserves the taser, no doubt as he was out of control with the other cops. No excuses, but maybe he thought the male cop was pointing a gun at his [I assume] brother? Hence the reaction on the male cop and the subsequent taser, which I understand.
The 'kick and stamp' was outside the contained situation and premeditated response to what happened to that team.
There is clear instigation and all reaction, outside of the rightful taser, are out of control by the assailants.
All the males, involved, need charging in my opinion.