a. Joe Pietersen kicks out for a line-out to the Stormers about 14 metres from the Hurricanes' line.
The Stormers throw to Andries Bekker and form a maul on him. They immediately move the maul forward and run it towards the Hurricanes' line. About two metres from the line, Thrush pulls the maul down. He is penalised and sent to the sin bin.
We shall come back to this incident.
b. Joe Pietersen kicks out for a line-out to the Stormers five metres from the Hurricanes' line.
The Stormers throw to Andries Bekker and form a maul on him. They move the maul forward but it falls apart about a metre from the line. The referee penalises the Hurricanes, saying that "1 and 7 had illegally defended the maul". 1 = Ben Franks; 7 - Karl Lowe.
c. Joe Pietersen kicks out for a line-out to the Stormers five metres from the Hurricanes' line.
The Stormers throw to Andries Bekker and form a maul on him. The Stormers move the maul forward and actually get over the line where the referee decides that they were held up. He then is informed by his assistant that Franks had pulled the maul down. Franks's action in doing so is clear and obvious as, down on his back, he pulls Bekker to ground.
The referee then talks to Conrad Smith, the captain of the Hurricanes, saying: "Another illegal collapse. 1 Gold. What I'm saying to you is that the next man who collapses down here - bin."
d. Joe Pietersen kicks out for a line-out to the Stormers five metres from the Hurricanes' line.
The Stormers throw to Andries Bekker and form a maul on him. They immediately move the maul forward and drive it over Hurricanes' line for a try by Rhodes
Let's go back to a.
Why is Thrush sent to the sin bin?
Thrush was guilty of foul play.
Law 10.4 DANGEROUS PLAY AND MISCONDUCT
(k) Players must not intentionally collapse a scrum, ruck or maul.
Sanction: Penalty kick
What Thrush did was an aspect of dangerous play. That is why he was penalised. But there is more to it than just a penalty.
Law 10.5 SANCTIONS
(a) Any player who infringes any part of the Foul Play Law must be admonished, or cautioned and temporarily suspended for a period of ten minutes’ playing time, or sent-off.
The referee has a choice of three ways of dealing with him - ticking off, yellow card or red card. In this case the referee issued a yellow card, as he is entitled to do.
Enough?
It does not seem that the referee considers a penalty try. He may have done so but it is not obvious.
Law 22.4 OTHER WAYS TO SCORE A TRY
(h) Penalty try. A penalty try is awarded if a try would probably have been scored but for foul play by the defending team.
Probably? Not possibly and not certainly. Even more than more likely than not.
The Stormers had run the maul for some 12 metres. They were all on their feet and there was no reason why they could not have run it two more metres - but for Thrush's foul play.
But there was no warning? There does not have to be a warning. A single act - not a repetition of foul acts - is enough for a penalty try to have been awarded.
And the same would apply to b. and c. above as well as a.
It is hard to see the grounds for not awarding a penalty try.
c. After c. the referee warns that any other collapse would result in another yellow card/sin-binning. This was after Franks had collapsed the maul but Franks was certainly in a precarious position. He had been penalised for collapsing a scrum - a dangerous act, included in Law 10 which deals with foul play. He then was penalised for punching, which is included in Law 10's paragraph on dangerous play. Then he was penalised for illegally defending the maul close to his line. Then he was penalised for collapsing a maul close to his line.
Rugby players have been sin-binned for less. After c. he was no even admonished.