he was apparently a homeless guy with drink problems who had been hanging around the kettled off area near RBS all day
if anything the policeman pushing him was doing him a favour - not a great idea to bimble about when they are clearing the area with dogs - doesn't look like they intentionally knocked him to the ground or anything more like they gave him a firm shove in order to get him to move on and he fell.
That would explain why he fell over then...As I said.
Laying a finger is one thing, being forced to the ground is another
Forced? He was pushed, then tripped over his own feet.