Technically, I don't think he engaged in violence first. One of the 3 men grabbed him, correct? Some would consider that the start of the physical force.
That said, even if he HAD started the fight, it still does not matter. He FLED. You do not chase after someone fleeing in an attempt to hurt them more. That is the exact moment all notions of "self-defense" go out the window. I'm honestly having trouble understanding how you can be okay with chasing after and beating someone close to death, regardless of what they did.