This is apparently what directly preceded this video.
http://www.youtube.com/watch?v=jMisHKQ8UaY

Ron Paul elected congressional delegate was arrested and subsequently injured by police after objecting to an illegal manipulation of convention rules by LAGOP chairman Roger Villere and the Executive Committee at the Louisiana State Convention in Shreveport on June 2nd, 2012. Shortly thereafter the remaining 111 elected Ron Paul Delegates and Alternates called for a rejection of chairman Villere and, in accordance to LAGOP rules and regulations, turned their backs to Villere and appointed a new, majority-elected chairperson. Villere responded by having the new chairman arrested, and unnecessary police force resulted in hospitalization of the newly appointed official.

Here is another angle on the video here.
http://www.youtube.com/watch?v=KJzV171zkdg

It's the very end of the video that is the most shocking to me of all when the cop tells the guy taping this he is going to confiscate his phone as evidence. Really?! That's insane, this has to end cops can't take your phone because you video taped them doing something they think might jeopardize their job. This cop clearly get's scared and then reacts by using a thinly plausible excuse to confiscate the man's phone and do you really think this would have seen the light of day again if he had?
This wasn't the only police assault that day too.(This was another man entirely, after this.)
http://www.youtube.com/watch?v=ofnSb9l9rwQ&feature=related

From YT:
Ron Paul supporter gets assaulted at LAGOP