Russ Spalsh is a drill rapper whose name is short for "Russian." "Gun lean" is a dance move that Russ has been flexing since he started rapping in 2016. The dance involves shuffling shoulders back and forth while saying "left, right, left, right" as if you're carrying heavy artillery, which is typical of drill's black humor.
Russ is of Caribbean origin and this song is a merging of drill and dancehall, which he calls "crashment." (The term is derived from "bashment" another word for dancehall music).
Manchester United midfielder Jesse Lingard mimicked Russ' "gun lean" when celebrating scoring a penalty against Cardiff City on December 20, 2018.
Ariana Grande's collaboration with Zedd, "Break Free" came about after the Russian-German producer overheard Grande performing at a label showcase while he was backstage, and he mentioned to his team that he wanted to work with her.