Hate to say it, but that's what I first envisioned about this kid, that he was a disrespectful punk. Why did he need to walk on this guy's lawn? I can understand it if it were the only way to get to his home. Somehow, I doubt that was the case.
It ticks me off when the parents of the kids at Halloween allow the kids to take a shortcut across my lawn instead of walking down the driveway. However, I think that I also did that as a kid (but my parents weren't with me).
That being said, the man should have just let it go. Eventually, the kid would have grown up and moved away. Now, two lives are ruined; and the man won't have any control at all over his lawn. I wonder if he now thinks that it was worth it.
ETA: I believe that this was an impulsive act. What separates humans from animals is that we are able to control our impulses. How many times have you wanted to ram a car that has just pulled out in front of you, causing you to put on your brakes? If we all acted on our impulses, this world would be even scarier than it already is!