It looks to me like he offered the kid a chance to surrender rather than being shot at close range. The kid proceeds to shoot him three times at close range, and he responds with one well aimed shot. While I don't advocate aiming to cause pain, the kid had plenty of chance to avoid this.
If you aren't mature enough to play paintball properly you shouldn't be playing.
This goes for both the folks in the video.
If it were me i wouldn't have even asked the kid to surrender and i wouldn't have shot only once. :-) But then again the guy was using a pump stock class marker on an indoor field so as bad as it looked, and i do feel for the kid, it was not that bad.
My father and I had this bonding moment. He took the igniter out of a gas grill, handed the electrode it to me, and started pressing the trigger. Why? Because it's just a lesson you need to learn about dad.