They tried detaining him and he resisted.
He was silently protesting, he has a right to. I think the security were just overzealous in their detaining of him for "suspicious activity". But really, are we really this fearful in our society, this paranoid, that silent protesters are "suspicious"? This is ridiculous.
In the next few years, if policing like this keeps up, we'll be on the verge of civil war and revolution. Our paranoia and the government's effort to patronize that paranoia will inevitably lead to a violent climax.