Rules player and fans need to understand.

[The Claw]

A lot of people seem to think "showing the ball" is breaking the rules, which is not the case.

[4father]

The shoulder tackle must be shoulder to shoulder.  People scream at the ref for giving a free to a player emptied by someone's shoulder... in the face or chest.

[AZOffaly]

The shoulder tackle must be shoulder to shoulder.  People scream at the ref for giving a free to a player emptied by someone's shoulder... in the face or chest.

And players tap their shoulders to say 'I hit him with my shoulder ref!'. Yes, yes you did. Right in the chops.

[4father]

The shoulder tackle must be shoulder to shoulder.  People scream at the ref for giving a free to a player emptied by someone's shoulder... in the face or chest.

And players tap their shoulders to say 'I hit him with my shoulder ref!'. Yes, yes you did. Right in the chops.

True!

[PAULD123]

The shoulder tackle must be shoulder to shoulder.  People scream at the ref for giving a free to a player emptied by someone's shoulder... in the face or chest.

I think the rule states it as "Side to side" but the common interpretation is that it should be shoulder to shoulder. Certainly you are correct it is not a case of shoulder to "any-other-part-of-your-opponent-you-feel-like"

Also it is only allowed to be done on a player:
(a) who is in possession of the ball, or
(b) who is playing the ball, or
(c) when both players are moving in the direction of the ball to play it.

Just running on and driving a shoulder into someone is a foul. Shouldering someone to prevent them moving into space is a foul. Shouldering after the ball is played is a foul. Shouldering someone who is running away from play (e.g. retreating defender) is a foul. And shouldering someone who is running to the ball to play it while you yourself are not attempting to get to the ball is also a foul.