"The news article at the top of this thread doesn't comment on...

"The news article at the top of this thread doesn't comment on any political affiliation. Why make the assumption?"

The assumption was made no doubt because it was originally reported by the press on the scene that the shooter was one of the Antifa protesters.
The press reporting was later clarified when Denver police issued a statement saying he was merely a security guard with no political affiliation. That lasted a few hours, til it emerged it was this bloke:




And rather than speculate from a still photo, you should watch direct footage of what happened. It tells a very different story than the single image you posted.

There was some lunatic in a "Black Guns Matter" shirt provoking the right wing protestors, literally yelling at them to attack him (which they didn't do). The shooter then inserts him into the situation, pulls a gun and executes his victim. The shooter was a psychopath. In no way did the victim attack the shooter, the mace was a last second defence against the shooter, not an unprovoked attack. Watch the footage..