When you use many speed boosts in a row to give you more speed then the game kicks you.
How to replicate:
Use like 25 speed boosts in a row and run.
Go to world: KingFish and try it out by yourself, it will kick you when you run while on speed boosts.
By kick I mean, getting kicked out of the world to the main menu loading screen and back to the world where you got kicked. Some call it Hack checked.