Master Yi, broken?

i played a PVP today around 10:30pm, and there was four of in a group. the players we against had Master Yi on their team and i think he is broken. 10 minutes into the game he only had bezerkers greeves and when he would hit any of my teammates, one hit would knock our health down to nothing. either he is broken or someone is cheating somehow but there is no way he could have all that damage 10 minutes into the game?