Getting movement on a fastball

I really am trying to get movement on my fastball so i tried different grips and pressure with different fingers and finnaly the ball did something… it went strait two the left (im a rhp) and didnt drop or anything… it appeared to of went to the left by like 2 feet… i threw it like 6 times in a row but then i had to go inside. The next day when i tried to do exactly what i did the day before my pitch did nothing. The way i threw it was by taking the ball like a two seam and by Sliding my fingers up the ball until you get to the two horizontal seams. then i put my thumb on the left seam on the bottom of the ball and put pressure with my middle finger and threw it strait over the top.
Does anyone know the name of this pitch… or what I can do To be able to throw it again

that sounds to me like a 2 seam fastball. i tried throwing it the same way you said but i dont get no movement at all, but i know you have to put pressure on your middle finger or the pointer one of those two to get movement. just keep on practicing it.

that sounds like a cutter

i think u have to ge tthe right arm angle or something… u should work on it two… ud be ammazzzeeedd by how much it moves… its literly like 3 feet… no joke. strait to the left

yeah if you are throwing it supinating your wrist its a slider, if you’re throwign it like a fastball its a cutter