I like to watch a commie get fucked just as much as the next guy.

That being said, it looks like the knife was sheathed. With my limited knowledge of the laws, I would assume that whoever maced the driver may have put themselves in a legally actionable position. The driver was not brandishing a knife; he was holding a knife. There's a big difference, and I'm sure a jury would take his side if he were to press charges for assault. @JustTheNews is right that we need more of the video to get a better grasp of the situation.