Coming into the Giro the favourites to win the overall race included Alberto Contador, Fabio Aru, Richie Porte, and Rigoberto Uran. At the start of Stage 9 on Sunday, as leader of the general classification, Contador held the pink jersey. Aru was four seconds behind him in second place. Porte was 18 seconds behind Aru in third place. Uran was in eight place 84 seconds behind Contador.
Towards the end of Sunday's stage, a brave solo effort by Tom Jelte Slagter was being chased down by a breakaway group. Behind this breakaway was the main bunch, including all the favourites. Then, with 12km to go, Aru made a move that resulted in three of the four favourites themselves breaking away from the main bunch. Missing from the group was Rigoberto Uran. The group comprised of Aru, Landa, Contador and Porte.
Despite having a teammate in the group, Aru soon realised he was unlikely to shake off Contador. Both realised that they had dropped Uran. Then a conversation took place between Aru and Contador. We don't know exactly what was said but from that point onwards the breakaway group worked together to put some time between themselves and Uran. The net result is that Uran fell a further 45 seconds back.
SKY's Richie Porte does not seem to have been part of the conversation and was a reluctant participant in the effort. Landa did most of the work at the front. However, when Porte refused to do his share, Landa dropped back and clearly indicated he was willing to sit on Porte's wheel unless he did some work. The commentators seem to think that Porte's shirking was more about maintaining his own position rather than any concern for the dropped Uran.
One could argue that Uran has nobody but himself to blame for not being in a position to respond to Aru's attack. Contador and Porte were covering such a possibility. I have not seen, nor read, criticism of the "collusion" that damaged a rival. Collusion between riders is par for the course. It is not seen as a problem. Breakaway riders will frequently collude to stay away. This is what happened on Sunday. It just so happened that that three of the four favourites were in the group. Acceptable competition in the cycling world is different from that in the business world.
That is not to say that the cyclists do not have rules on these things. Cyclists do not tend to attack each other around feeding stations or when there is a call of nature. Cyclists usually slow the pace to allow those involved in a crash back into the race. Earlier this year, the peloton was split by a train barrier descending during the Paris-Roubaix race (here). Those on the favourable side of the barrier allowed the others to catch-up (after some prompting). However, these informal rules can be interpreted in different ways. In the 2010 Tour De France, Alberto Contador took advantage of a mechanical failure to the bike carrying the Yellow Jersey and Andy Schleck. Schleck was upset and labelled Contador's behaviour as "unfair" and threatened "revenge" (here).
Schleck was clearly upset by Contador breaking an unwritten rule. Contrast this with Schleck's reaction to Contador being stripped of the 2010 Tour de France win because of breaking the written doping rules. Schleck was installed as winner. Yet, Schleck was reported as saying that for him Contador was always going to be the 2010 winner (here). Slightly strange but definitely unsurprising.