Scogin was crossing the street in a crosswalk. The UI Police officer claims that he placed himself at risk by stepping into traffic. The police officer flashed his lights and called out to Scogin to stop. It's pretty clear that Scogin can't hear him. The officer claims that he was "a runner" and chased after the student.
The officer caught up with Scogin and tried detaining him, asking if he'd had anything to drink. The student said that he was just walking home. The officer decided to detain (i.e., handcuff) Scogin. It's not entirely clear what happened next due to the distance, but the officer tackled the student. Scogin then repeatedly called out "My hands are already on my head, my hands are already on my head!" Meanwhile, the area was swarmed by additional police vehicles. Three other officers ended up piling onto the student before everything was completed.
You can watch the video here:
The UI Police officer later told the other officers that Scogin tried running, which isn't evidenced by the video.
I was watching a story about this on KWWL earlier this evening. Scogin showed how the officer listed him as being Hispanic in the arrest report despite two corrections by Scogin himself that he isn't Hispanic.
Grayson Scogin was taken by his girlfriend to the emergency room the next day and was treated for severe bruising.
He was ultimately charged with public intoxication and interference with official acts.