Wrong approach. Have a confederate with a video camera nearby. This confederate must be undercover and look like the enemy. No sports logos and dirty clothing ripped in a few strategic places if a guy two days unshaven.
Get it on film and under no circumstances strike back. Leftist live to get jailed conservatives do not. If your group is creative and you follow instructions you can even sue Code Pink or whatever organization the offender is a part of. Maybe Mark Levin could even be enlisted as council and you can get extra publicity for protest warriors.
believe...I was only kidding- I spent most of the first week of September in Manhattan battling this scum with Protest Warrior and a few fellow freepers during the RNC.