So I was recently watching this video and I'm kind of left wondering why the cop doesn't just kick the leader of the pack down the stairs. The guy looks frail enough that the cop could've easily applied enough torque to make the guy lose his balance, which could serve both as a physical obstruction to continuing to climb that staircase and a deterrent against continuing to do so... especially if the falling leader of the pack ends up knocking over other rioters like dominoes.

This is a question of psychology, not physics