He he he another misconception. You can tackle from behind provided its a legal tackle i.e. you don't commit a foul in doing so. I hear that one a lot.
'Oi ref, he's tackled him from behind!'
'I know...and what a bloody good tackle it was too!'
Another misconception that annoys me is the "I was going for the ball/got the ball" call. Like if you fly through someone at knee height with both sets of studs up its ok as long as you were trying to get the ball...