Clip 1 - 7 June 2019 - Law 9
Marika Koroibete gets the ball near the Waratahs' 10-metre line. He races downfield as desperate Waratahs try to get to him. Just short of the left corner, Curtis Rona, the Waratahs' left wing, gets to Koroibete and bangs into him, knocking the Rebel to ground.
Koroibete gets the ball back inside but the handling goes awry. The referee awards a scrum and then, after examining the evidence, he penalises Rona for an armless tackle.
Rona does bash into Koroibete, upper body against upper body. Rona makes no attempt to encircle Koroibete with his arms. In fact his leading arm, his left one, is tucked bent against his own chest.
Just before this match, World Rugby had sent out a directive intended to make dangerous (high) tackling easier to sanction. This is one of the directives for the award of a yellow card:
In the case of shoulder charge to the body without contact with the ball-carrier's head or neck with low degree of danger, the referee will show the offender a yellow card, i.e. send him off the field for 10 minutes or whatever length of time applies to the match.
Law 9 (abbreviated laws) deals with foul play.
Law 9.16: A player must not charge or knock down an opponent carrying the ball without attempting to grasp that player.
Rona charged and knocked down ball-carrying Koroibete without attempting to grasp Koroibete.
That is foul play - and right at the goal-line. There is a case for a penalty try.
Penalty try: Awarded when, in the opinion of the referee, a try probably would have been scored (or scored in a more advantageous position) if not for an act of foul play by an opponent.
Rona acted illegally. He did not act legally. There can be no knowing what he would have achieved if he had acted legally because he did not do so.
Rona's action stopped Koroibete from scoring. Simply put, he prevented by foul means the probable scoring of a try.
That means penalty try.