Correct... If he was just running away. That wasn't the case here and not what the video clearly shows. The second he turned around with something in his hand that can potentially harm someone or you in any way, which again is what the video shows, that's where he fucked up and posed a threat to the officer. He literally fought them off, ran and turned around to shoot the taser. You can argue all day how much of a threat that posed, but if the officer felt threatened, he had a right to protect himself and his partner. I'm not someone who stands up for cops at all but I'd be surprised if they get convicted.
Like you said, a lot could have happened that didn't, but in that moment you think the cop was supposed to wait and see how things played out. Would you? If you were standing there with your child or your wife, and a dude you just tussled with ran off and turned around to shoot something at you that has the potential to harm you.. what would you do? If it's me, I'm squeezing my trigger.
I'd claim factually (which is on video) that I was threatened and was protecting myself, family, or partner from harm. If a jury convicts me, then so be it. I'd rather know that I protected myself, family or whomever, than to have mofos crying over my casket.