In Super Smash Melee, controversies have long existed over the legality of modifying controllers, with different tournaments and cultures making different restrictions and allowances.
Brian Funes 2017, “Controller Mods: What They Are, and Who Uses Them”:
While most sports like basketball and football have a standard sized ball, other sports like baseball and tennis have a general regulation for their bats and tennis racquets, giving the players some wiggle room in customizing their equipment. Melee falls into this second category, albeit rather unintentionally. The line is clearly drawn concerning features that are banned in competitive play such as having macros or a turbo button, but when it comes to features a player is allowed to have on their controller, the standard is not defined. Modifications such as button feel and control stick gate modification fall into a grey area which haven’t been adequately addressed as of yet.
Not everyone is happy about these modifications though, seeing some of the notches as an unfair advantage — the “perfect wavedash” notch being one of them. The issue of fairness and having access to unfair resources compared to other contenders competing with a standard setup is another concern. If certain types of modifications are allowed, where is the line drawn?
This discourse is complicated by the fact that manufacturing defects on out-of-box GameCube controllers makes some of them inferior devices, such that modification can perform a leveling function, as much as giving an advantage.