Coach Menges explained it one day.
He said bush league referred to a coach or player trying to get an advantate in a way that was obviously beneath them, their level, or accepted baseball practice.
He would include intentional cheating (see: A-Rod),managers or coaches knowingly lying to umpires (see: Gardenhire), and Little League type plays and maneuvers.
Coach Menges' players left the program with respect for the Game.