Yea he was helping but because he hit him which was way unnecessary I see why the police took him down. Which he would be charged for battery. You can use force against others if your life is in danger and as long as you don't take it too far. But he was only a bystander and took it too far.
"Holding anger is a poison. It eats you from inside. We think that hating is a weapon that attacks the person who harmed us. But hatred is a curved blade. And the harms we do, we do to ourselves."-Mitch Albom