I read in a book that to get movement on a 4-seam fastball you have to put pressure on your index or middle finger. Will this sacrifice speed?
Or you could just throw a 2-seam. Mine moves quite a bit and I just hold it along the seams with no added pressure. You should try it!
One day, while warming up for a game, I suddenly let loose with a pitch that I had no idea was doing anything, but it was quite a bit faster than my other stuff, and not knowing what else to call it I called it my “whoops” pitch. When my catcher noticed it and wanted to know if I would care to try it in the game, I did so, and I discovered that it really got the batters screwed up! Later on I talked to Ed Lopat about it, and he got a stopwatch and timed me, and he let me know that what I had was a good 81MPH four-seam FAST BALL! It had a lot of movement on it, and I found that it didn’t make any difference whether I put pressure on it with my index finger or my middle finger, it just moved, and I was happy to add it to my burgeoning collection of pitches. Lopat told me, “That’s a good pitch. Use it. You can spot it—tease the hitters with it and throw them off balance—use it to set them up for your slider.” And so I did.
So I say, it all depends on how you feel; you can do it either way. Just be sure to stay away from the middle of the plate!
A great example of someone who put pressure on his fastball during his career is Greg Maddux.
I would say if you do it correctly (get movement - in, out, down) that you will loose some velocity. The exact amount will depend, but by the simple fact that you are trying to get the ball to move, I think it’s fair to say that the velocity will suffer.
if you want more tailing action use your index finger and for sinking action use your middle and for other movemnet make your fingers off center.