(V):  Id say the guy was provoking the police by his actions.  And in a tense situation like G20, that was a stupid thing to do.  But police are supposed to show restraint.  Shoving a man to the ground was way out of line IMO.  Arrest him yes, but physically assault him?  The police officer lost his cool.   If in fact that action caused the man's death, then by definition of the law, that could be manslaughter. 

OTOH, why couldn't the police officer simply have ignore the man.  He was not a threat.  He was just moving slowly.   Eventually, even a turtle makes it across the street.