Minor Hockey is serious business, especially to this coach in Canada where these children were playing at the University of BC.
Apparently, one 13 year-old player on the opposing team just didn't suffer enough after the coach mocked him throughout the game and decided to use the post-game handshake as an opportunity to get revenge for his middle-finger response.
Taking a page from The Karate Kid's evil sensei, John Kreese, he waited until the child's back was turned and went on to "sweep the leg."
You see, if he was a real tough guy, he would have attacked the 13 year-old child face-to-face. But, alas...