If I asked you to do just 2 things - flash the knob to the pitcher OR flash the knob to the opposite batters box - not pulling/pushing the knob, just flashing. Sounds easy, right? If I asked you to only flash the knob at the pitcher when I say "fb in" AND I ask you to flash the knob at the opposite batters box when I say either "fb out", "breaking pitch". Could you get good at that? Now I want you to go back and look at video. Look for swings where the hitter got a fb in. Watch where he flashes the knob. Look for the fb out OR breaking balls - watch where he flashes the knob.
Hmmm...that sounds a lot like "knob to the ball".
Then, a coach overhears someone using that simple cue, applies it literally, over-bakes he hell out of it, and has his hitters do this...