Many years ago I was in Seattle in my car stopped at a light when a "mob" of marchers came down the street and passed my car. It was scary and at that time, with a nice car, I thought I'd be targeted. I did not get out of my car.  It is totally inappropriate for any marchers to even touch a vehicle as some did in Eugene. And though legal, I don't advise anyone get out a yell at protesters as they pass. 
This is what I think we know: Marchers broke off from the main march. They passed a few vehicles in the street. The marchers were aggressive toward Sparkhawk's vehicle. Sparkhawk got out and cursed at the marchers using and anti-gay slur. He says those comments not express his views. He had a momentary "knee-jerk" reaction that caused him to press on the gas but he had no intention to drive into the crowd. He felt nervous and especially so when he got out of his car. 

Police are investigating and may issue citations.