While I was reading the Laws of the Game to look for an answer to another question, I came to read the following bit:
Cautions for unsporting behaviour There are different circumstances when a player must be cautioned for unsporting behaviour, e.g. if a player:
...
uses a deliberate trick while the ball is in play to pass the ball to his own goalkeeper with his head, chest, knee, etc. in order to circumvent the Law, irrespective of whether the goalkeeper touches the ball with his hands or not. The offence is committed by the player in attempting to circumvent both the letter and the spirit of Law 12 and play is restarted with an indirect free kick
This goes against all my knowledge of football, as it happens on a regular basis, as a matter of fact it's even a sign of a good defender to do this properly. Have I misunderstood something, or is this rule just not enforced on a regular basis?