I think it's about the fact that the regulations are based in Smogon.
This move was banned year 2014 by a vote of the heads of Smogon.
U can see votation here > Voting on the move Swagger.
The post where all the reasons were explained, is no longer accessible in Smogon, but ere are some of the main reasons:
- Contoneo / Swagger is not competitive on Pokemon, even without the Prankster / Prankster skill.
- That the Steel Type lose its resistance to the Sinister Type means that Foul Play is incredibly powerful
- Teams-Swag (teams based on Swaagger) can play without any necessary knowledge of the metagame and is a 'tactic' that is being followed quite a bit.
- The Pokémon with the Own Tempo are not viable in the OU.
- Lum Berry is not an effective counter against "swaggers spammer"
- Combined with Ditto equipped with Choice Scarf you are able to copy the boost that Swagger has caused the opposite team without copying the confusion and cleaning the whole team.
Remember this game is constantly being updated, and although in this list I mention several things that are not yet working, the goal is that in the future if they are. Because of this, the banned swagger was the only way, because we are usually playing under the tier OU. (In Smogon swagger is permitted in Ubers, and Dobles, VGC, o BattleSpot).
:Smile: (sorry for my english, I hope it has been understood)