I have one son who plays attack and has been taught how and when to properly take a behind the back shot, and if you don't practice it and use it in a game as a 4th or 5th grader you wont know how to do it when you are older and it is the correct shot, the object of the game is to score. however if he did it in a 10 - 0 game I would have a long sportsmanship talk with him on the ride home. I also have a son who plays goalie and I encourage him to run the ball up field when appropriate and he has taken a few shots because he was never picked up, again if you don't practice this in PAL and over the summer you will not have the ability to do it in HS when you might need to.
While I would never encourage "going after" a kid on the other team for taking a behind the back shot, if it was a 10 - 0 game and the kid did it, I wouldn't be upset seeing a D putting him on his butt, not to hurt him but to let him know it wasn't appreciated, when this happens as a continuation of a play it is a lot more acceptable then when it is per-meditated and coached.
Not all behind the back shots are the same and many are not hot dog but the correct shot. | 
