The ball goes forward off the hands or arms of a player and hits the ground or another player. Results in a scrum with the put-in to the opposition.
The ball fails to travel backwards in a pass. Scrum to the opposition.
Ball not released:
When the ball becomes trapped in a pile-up of players, a scrum is awarded to the attacking team if the ball is in contact with the ground and to the defending team if it is held up off the ground.
Scrums can also be awarded if the ball is not thrown into the line-out straight; a restart kick is carried incorrectly; the ball is thrown into the lineout incorrectly; a player carries the ball over his own try-line and touches down in-goal; for accidental offside; or a scoring player fails to ground the ball properly in the in-goal area.
Hideously complicated. Basically, players not involved in rucks, mauls, scrums or lineouts must remain behind the back foot - that is, behind the last attached player.
Penalties are awarded for serious infringements like dangerous play, offside and handling the ball on the ground. It is signalled by the referee with a straight arm raised in the air. Players can also receive red and yellow cards, as in football.
The offending team must retire 10 metres for both penalties and free kicks. A team can either kick for goal, run the ball or kick directly into touch with the resulting line-out awarded to them.
This is a lesser form of the penalty. A team cannot kick for goal (unless it is a drop goal). The normal 22m rule applies for kicking for position from a free kick. It is signalled by the referee with a bent arm raised in the air.