Role of policeman

take a look at the following video

http://www.youtube.com/watch?v=rSxSlT2M76s

This takes place in my school, one of the main buildings that has most flow everyday.
I am not going to comment on the person who is been arrested, because I don't really know what happened.
I did not get a chance to see scene inside the building. But I was outside of the building. I saw five police cars and at least 15-20 police officers in from of the building, as well as an ambulance.

My friend saw it in person, close to the scene.
After I saw the video and heard his decription. All I think of is that... why those policemans have to beat up the crime so much? (maybe not a crime, he was just drunk.) There were more than enough police officer there to control him. Is it really necessary to hit him that many times.

Maybe I should not comment just base on what I saw and heard. I am sure there is something inside that I wouldn't know. However, I don't agree with polices use violent action easily.