Here's the link
http://www.guardian.co.uk/uk/video/2009/apr/07 /g20-police-assault-video
There is no decent sound
it looks as if he is ambling along infront of the police, they tap him on the shoulder and he doesn't move along.
It looks as if he's ignoring them and being obstructive.
One of them give him a shove and he falls because he has his hands in his pockets
It doesn't look all that unreasonable - he's getting in their way.
On the replay you can see them hit him on the legs with a baton - first it doesn't look that hard - he doesn't take his hands out of his pockets!
On the ground he's remonstrating with the police - he doesn't look hurt.
It's only the fact that we know that he died later that causes us to react this way.
If he had just gone home and someone had posted this as "police brutality" I think there'd be an outcry of "hand wringing liberals"
I don't think this is particularly excessive