Warning: SPOILERS ahead for Cobra Kai season 3.
Cobra Kai season 3 saw Hawk finally break free of John Kreese's brainwashing and switch sides — and, though the turn seemed sudden, it actually made all the sense in the world. Played by Jacob Bertrand, the character was initially known as Eli Moskowitz. Similarly bullied and inspired by Miguel Diaz's karate prowess, he also signed up for the tutelage of Johnny Lawrence and his doomed version of Cobra Kai. There, Eli was encouraged to "flip the script" and completely overhauled his image.
As Hawk's karate skills increased, however, so did his arrogance and aggression. He distanced himself from his best friend, Demetri, and such passions as Doctor Who. Eventually, those efforts saw him become a bully in his own right. After the school brawl in the Cobra Kai season 2 finale, he committed fully to the more extremist teachings of John Kreese. However, Cobra Kai season 3, episode 10, "December 19" saw him experience a change of heart. Saving Demetri, Hawk joined Johnny and Daniel LaRusso's newly-combined dojo. Some have since declared the move to be too sharp and too sudden — but the signs of increasing dissent were there all along.
The problem with binge-watching is that there's little time to process one episode before enjoying the next. As such, it would seem like Hawk was a firm proponent of "Cobra Kai for life" until he suddenly wasn't. In truth, though, he was already torn between his true, nerdish self and new hardcore persona last season. And he questioned Kreese's decisions from the start of Cobra Kai season 3. He'd remained loyal in the erroneous belief that Kreese was just as loyal in return. Having absorbed Kreese's war stories, Hawk assumed the traditional "leave no man behind" mantra was inherent to his mentor's core. He quickly learned that that wasn't the case — when longtime students like Bert and Mitch were unceremoniously expelled. With his qualms disregarded, Hawk also repeatedly learned how, even with tough love, Johnny had been more receptive.
Part of Hawk's continued support was also the notion that Kreese could eliminate any lingering weakness. Hawk took so to heart the idea of simultaneously wreaking vengeance on Miyagi-Do Karate and not making Miguel's mistakes, he actually broke Demetri's arm. At that moment, however, Hawk's mindset snapped just as firmly as Demetri's bone. Hawk had been in the same position as Miguel when he showed mercy to Robby. By actually following through with the brutal act, though, he got to see why Miguel might've been right. Vengeance was achieved, but he felt no actual joy or triumph, no sense of strength. As such, the schism only grew wider between who he wanted to be and who he actually was.
It also became clear that he was more like his old friends than he cared to admit. Similar to how Burt couldn't feed the mouse to Cobra Kai's pet snake, Hawk couldn't bring himself to handle such reptiles. At that moment, he realized he was surrounded by people he hated (Robby and Kyler). Furthermore, he saw he was little like them and rapidly being usurped. Though he would report on Johnny's new Eagle Fang dojo, it was a final desperate attempt to cling to his current status — though he already knew deep down that he no longer belonged.
Hawk actually spent the Cobra Kai season 3 finale not really engaging his closest former friends in battle, not as invested as usual. In those moments, he accepted that Kreese only cared about victory and could easily turn on him too. Conversely, Hawk saw how former Cobra Kai, Eagle Fang, and Miyagi-Do supported and protected each other. He saw that friendship and loyalty built on love were stronger than when maintained through fear. However, though Hawk only officially turned upon seeing Demetri in a similar position as when he'd broken his arm, it was still built on a foundation of season-long inner turmoil. Fortunately, now back by Demetri's side, Hawk could find a proper balance in Cobra Kai season 4 — and realize that one can be both a nerd and tough as nails.