It doesn't matter if it's a 14 year old kid or a 65 year old grandfather. These types of actions are not acceptable in any situation that I can possibly see on an airsoft field.
As already stated, this is a game of honor, fun and some competition. Getting pissed and beating on guys that you may be playing with instead of against the next time is just stupid. There is no excuse, and no way that you can say that his actions are understandable in anyway because if you can understand them maybe it's because you're like him????
Everyone gets pissed sometimes, as adults we should know how to react properly and our first instinct should be to protect our kids not beat the living hell out of the guy on top of him. It should be protection NOT revenge. Is that what you want your kids learning? That it's not ok but it is understandable to just run up and punch some guy in the head?
Guys, we play dress up and shoot each other with bb's... we do it on our own time for fun.