Looks like they didn’t like him taking their picture with his cell phone.
I just posted this story in a Flickr Group named Photography Is Not A Crime.
We document lots and lots of stories like this.
http://www.flickr.com/groups/photography_is_not_a_crime/discuss/72157624767793976/
As they approach this guy, he starts video taping them with his cell phone, and that caused him to get beat down and arrested.
I'm very much pro LE, but this is bullsh*t and I'm tired of seeing citizens being treated like some foreign enemy.