“So what was the officer to do, allow Massey to knife, hit, shoot, kick, spit on him before defending himself?”
Have you actually watched the video?
The man was not threatening the officer, and in no way appeared threatening.
In general I support cops, but this was WAY over the line.
He was also not doing what the cop repeatedly told him what to do (Turn around, hands behind your back etc.).
How should the cop have gotten the man to cooperate?