For making a sound.
This is horrible. The man was not resisting or being combative in any way. Video shows that the man simply made a spitting noise, trying to clear something from his lip, that's when the out-of-control cop has a meltdown. After his head is slammed against the concrete blocks and throat is grabbed, he goes in and out of consciousness. To top it off, the other officers lied on the report saying the man had been combative. Video shows he wasn't.