Cobra Kai season 3's finale featured an all-out battle between the combined Miyagi-Do/Eagle Fang Karate dojos versus Cobra Kai but originally, the students of West Valley High weren't supposed to wreck the home of Daniel LaRusso (Ralph Macchio). Instead, a different and beloved location from The Karate Kid movies was intended to be the kids' battleground before logistics forced a change.
In Cobra Kai season 3's finale, "December 19", the students of LaRusso's Miyagi-Do dojo and Johnny Lawrence's (William Zabka) newly-formed Eagle Fang decided to join forces, unbeknownst to their senseis, who were at a country club enjoying a Christmas party. Miguel Diaz (Xolo Mariduena) and Samantha LaRusso (Mary Mouser) rekindled their romance and teamed up to stop the cancelation of the All Valley Under 18 Karate Tournament. In "December 19", Miguel brought fellow Eagle Fang students to Sam's house where they agreed to combine their dojos. Cobra Kai students then committed a home invasion and attacked their enemies, but the fight saw Hawk (Jacob Bertrand) have a change of heart and quit Cobra Kai while Miguel faced off against Kyler (Joe Seo) and Sam took on her arch-nemesis, Tory Nichols (Peyton List). When Tory saw Hawk had defected and the tide had turned against Cobra Kai, she retreated, leaving the LaRussos' home wrecked.
However, Cobra Kai season 3's climactic battle between Daniel, Johnny, and John Kreese's (Martin Kove) students was supposed to take place at the Miyagi-Do dojo, which is located at the home of the late Mr. Miyagi. While the actual house Miyagi left to Daniel-san upon his death is mostly empty and converted into a dojo, the backyard features a lush garden and a koi pond. It's the idyllic environment that evokes Miyagi's home of Okinawa that Daniel trains his students in. But, as Cobra Kai's stunt coordinators Hiro Koda and Jahnel Curfman revealed to EW, the reason the location was changed was due to inclement weather. The producers considered setting up rain towers and staging the climactic fight in the rain but while that would have been visually striking, the reality of a dozen young actors and stunt people shooting at night outdoors and in mud made that idea unworkable.
Instead, the decision was made to switch the fight's location to the LaRusso home, which had an even greater advantage of being an interior set the production could fully control. In Cobra Kai season 1, the LaRussos' home was an actual house they filmed in but in season 2, the interiors were reproduced on a stage. By moving the fight to Sam LaRusso's house, it gave the production more freedom in terms of hallways, corridors, rooms, corners, and nooks to make the fights between the teens more varied. Plus the producers gave the green light to smash up the set as much as they wanted, which heightened the chaos. The production also shoots these brawls as "oners" to get as much of the fighting in camera in a single take as much as possible, which would have been harder in the rainy exterior of the Miyagi-Do location.
Cobra Kai season 2's climactic fight at West Valley High escalated the level of violence in the series but that showdown was also an epic crowd-pleaser that season 3 had to try to top. Moving the fight to the LaRusso home heightened the fear for Sam, who had PTSD and dreaded facing Tory Nichols again during season 3, since it was the sanctuary of her own home that was now being violated by Nichols and Cobra Kai. Tory and Sam actually fought in the gardens of the Miyagi-Do dojo earlier in Cobra Kai season 3, where Nichols tried to drown LaRusso in the pond, but that was actually a nightmare Sam woke up from. Relocating the finale fight to the LaRusso home also leaves Miyagi-Do free to be a possible location for another melee in Cobra Kai season 4, although longtime fans of The Karate Kid movies also dread the idea of Mr. Miyagi's home being destroyed by Daniel-san and Johnny's students and their enemies.