Law text
16.2 JOINING A RUCK
(b) A player joining a ruck must bind on a team-mate or an opponent, using the whole arm. The bind must either precede, or be simultaneous with, contact with any other part of the body of the player joining the ruck.
Sanction: Penalty kick
10.4 DANGEROUS PLAY AND MISCONDUCT
(g) Dangerous charging. A player must not charge or knock down an opponent carrying the ball without trying to grasp that player.
Sanction: Penalty kick
(h) A player must not charge into a ruck or maul. Charging includes any contact made without use of the arms, or without grasping a player.