Of course it can. But how often do you see a leg being broken in a completely fair challenge compared with the numbers you see from either two feet being used or a foot at shin height... Think about it for a minute from a different perspective. As a player, would you want someone coming in at you like this? No chance. As referees, it's our job to protect the players as well as ensuring the game is played within the confines of the laws. If I was in a situation where someone went in like this, red all day long.