This is real. It happened to me, too. Years ago, I was playing a public course with my son. We were on the 18th fairway when one of a threesome whistled a drive past my ear from the adjoining hole. My son yelled at them to call fore (it was an obvious banana ball). They gave us the finger, so my son hit it back at them and almost got'em (he's a good golfer). We finished the round with no further incident and drove to the parking lot to pack up and go.
As we were loading our clubs, these three came running at us. The guy who had driven the ball ran right up to my son and punched him on the jaw. Unmoved, my son fired back instinctively and hit the guy in the head, knocking him down. My son was a Marine with hand to hand training and mma skills. I ran up to him with my back to the guys, the other two of whom stood in shock. I begged my son in a loud voice not to hurt them, then turned to them and told them that they didn't know what they were dealing with and they should go. The guy picked himself up off the ground and got in a fighting stance, but the other two grabbed him and pulled him away and off they went. None of the three would have stood a chance. On the way, I chided my son that he just took on the one guy and left me with the other two. That incident is now a part of family lore.