Here is the surveillance tape of the awful fall. Riley's fall happens quickly once he comes into frame. The video begins with him jogging. If you slow it down to .5 speed, you can see he trips, his body leans left, and when he is falling his head hits the metal pole. His body limply slides down the pole. It takes him a while to shake it off and get up off the ground, then we see him hugging the wall as he walks away. His head is down and his neck is bent over maybe in an effort to read his phone.
I'm willing to be corrected if anyone sees otherwise.