well.... the antecedent is missing so this video means shit with it however, watching the video as is:
people seem to not realize that if a cop legal detains you, you must comply with the officer(sitting in your car, in the back of their cruiser, in cuffs). this is a their discretion. you have the right to remain silent, but not the right to avoid being detained) however you are being detained.
arm chair quarter backs are clueless when it comes to managing physical behavior, so if you have never wrestled or been in a physical fight you dont know jack shit.
the officer given the circumstances was professional in my opinion. of course you can try and hold someone to a impossible perfect professional standard. like I said before you dont know jack shit unless been in the situation. this is a fight or flight response of the officer and he is managing his life/safety. the officer pinned him. the suspect continued to not follow direction of stop moving since his feet/legs are moving and more than likely the officer has also contained his arms. as you noticed an observer asks the officer if he needs assistance and goes towards the suspects feet. the suspect continues to twist. officer pulls the taz since he is continuing to move and the officer may be losing control of the suspect(thats really bad when a suspect over powers a police officer as it could escalate even further). he warns him he will light him up(in an ideal world when you are not fighting for your life or from a text book "sir please remain calm and stop moving, if you continue to resist I will have no choice but to use non lethal force aka taz). the bop on the head is completely reasonable as it wasnt hard and its less intrusive than the taz. the bop on the head can focus and intimidate someone to calm down and stop whatever shit they are doing. cops are intimidating since they carry weapons, wear quasi military uniforms and are typically big men. as a former insert job here. taking down an adult male with a woman as a second pretty much means you are on your own. they are typically useless except for the rare woman who is built like a line backer(they do exist but they are rare). one of my female coworkers was like this(mid 200s 6 feet tall and solid), not overly feminine imo but in that situation muscle and size are number 1. officer looses taz(this is really bad). officer applies more force(crushing the suspect). this is highly uncomfortable and painful but tends to work very effectively instead of beating them with a baton across the head. he would had tazed him instead if he didnt drop the taz.
the suspect will have minor scraps and bruises.
this cop was professional based upon the video supplied. perhaps if there was video from start(cop stops kid) I would have a different opinion.