The cop who was hit seemed to run away.
The cop standing next to him seemed to have no reaction.
In all fairness, this is Seattle. Most of those cops probably voted for the current mayor and governor, and many of them might even support the riots.
I don’t have time to review the video, but what I saw was a line of bike cops and this guy got separated from the group. Rioters grabbing at his bike, tossing stuff at him, then he got clobbered up the side of his head.
Those people standing there look like cops because of the dark outfits and professional looking helmets, but I think they were all rioters.
I’ve seen various videos about antifa tactics. Picking off the last cop in a line would make sense.