Robby has a difficult time throughout season three, and he doesn't have a redemption story like the other characters do. The season starts off with Robby nowhere to be found, since he took off after the big karate fight that left Miguel in a coma. Johnny and Daniel team up to find him, eventually finding him at his mother's rehab facility after countless failed leads. Daniel calls the cops and corners Robby, leading to Robby spending most of the season in a juvenile detention centre. There, he tries to spend most of his time laying low by reading and serving in the soup kitchen, but is cornered by bullies, and disappointed by his dad Johnny that fails to show up when he says he will. Robby continues to despise Miguel, feeling abandoned by both his dad and Sam for him.
Robby cements his role as being on the dark side in this season, teaming up with the bullies in the juvenile detention centre, and going straight to Kreese and Cobra Kai once he's out. His rage towards Johnny, Daniel, Miguel, his own mother, and Sam is evident, and it goes perfectly with Kreese's philosophy. By the end of the season, a fight occurs at Cobra Kai between Kreese, Johnny and Robby that ends up with Johnny knocking Robby out. By the end, Robby has abandoned both Johnny and Daniel, and is 100% on team evil, aka Kreese and Cobra Kai.