No one is above the law, regardless of if you're an average person or an Olympian. In the eyes of the law, Kerley is nothing special.
The police were just doing their job. It's Kerley's fault for getting arrested. Kerley was acting pretty stupidly and was impulsive. You should never act aggressively to a police officer and should treat the police with respect. If you attack a police officer like Kerley did, you're asking for trouble. Playing "tough guy" against the police doesn't work.
Had he initially remained cordial and complied with the officers' requests to stay out of their active crime scene investigation, it wouldn't have escalated to him being tased, wrestled to the ground, and arrested. Kerley and his girlfriend should have just walked around the area to get back to his car, or as other posters mentioned, just take an Uber and get the car in the morning. Though, him being presumably drunk didn't help him stay calm.
I will say, however, that the officers should have respected the fact that Kerley is a professional athlete and avoid roughing him up too much.
On an unrelated note, I recall Tyreek Hill was also arrested a few months back.