I don't know that the police did anything improper since he was clearly resisting arrest. However, it is another example of people resisting the police and shows the difficulty this creates for officers and the typical escalation of force. These officers ended up punching him in the face and pepper spraying him. Fortunately, these officers made some effort to dial back the force they used and eventually the young man complied. Notice the role of the on lookers in videotaping, demanding the police to use restraint and urging the young man to comply.
More details of the case can be found here.