i want to learn how to throw a cutter. how should i grip it, throw it, and use it (against a batter)?
I grip my cutter like this, and when you throw it, throw it exactly as you would a fastball, just with extra pressure on the ball with your middle finger.
When facing a lefty(assuming you’re right-handed) you can start a cutter over the plate, only to have it run in on their hands, or try a sort of “backdoor” cutter and start it off the plate and have it finish on the outer corner.
Against right handers you can start it over the outer half and let it finish off, usually causing a swing and miss, or a weak hit off the end of the bat.
Some cutters, depending on your grip, arm slot, etc. will move more vertically than laterally, and if this is the case you can throw it over the bottom part of the plate and finish off, or use it like a sinker to get ground balls.
With hope this helps.