Arm angles

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depends on the batter

Depends on the batter and the pitcher, and probably most importantly the stuff he has. Flat mid 70’s fastballs and hanging breaking balls get hit no matter what angle there coming from. However having said that, I always see certain “molds” if you will when it comes to power pitchers. The high 3/4 righty who throws hard with a sharp 12-6 curve AKA the Nolan Ryan mold. The lefty who throws 3/4 or low 3/4 with a hard tailing fastball and a biting slider, a Randy Johnson type. I often just notice that certain stuff/arm slot combos mix well with certain breaking balls.

Right you are!!!
The arm angle doesn’t make any difference. What matters is how your stuff is working. If your curve ball hangs, or your slider is flat, or the knuckleball refuses to knuckle, the batters will just eat it up. Even your fast ball, if it’s lost some of that hippity-hop, will get chewed up, especially if you can’t keep the ball away from the batter’s wheelhouse. Do you remember the fourth game of the 1996 World Series?
Eighth inning. Braves leading Yankees 6-3. Mark Wohlers, the Braves’ closer at the time, had two runners on and one out, and Jim Leyritz, who had come into the game to catch in the sixth inning, was now at bat. So Wohlers came in there with a 98-MPH fast ball—and Leyritz fouled it off. And suddenly Wohlers was thrown off the track. He was confused, discombooberated, worried stiff that he might not be able to get this batter out with his fast ball. He went to his curve. Leyritz wasn’t biting. Another curve—Leyritz wasn’t biting. Wohlers came in there with a 99-MPH fast ball, and Leyritz fouled that one off. So Wohlers said the hell with it and tried a slider—and Leyritz fouled that one off down the third-base line. The desperate Wohlers came in there with another slider—and this one hung, and Leyritz was ready for it, and he blasted that pitch over the left-field wall to tie the game.
The thing to remember is something that Ed Lopat was always telling pitchers, and sometimes he had to tell them more than once—“Never the same pitch, never the same speed, never the same location.” He told me that in the course of a casual conversation about pitching to the hitters, and for me that stuck. He said, “Move the ball around—high, low, inside, outside. Change speeds.” And he interpolated something I never realized was a powerful suggestion: "And you know how to do that.“
And speaking of pitches, here’s what my repertoire was like, including the delivery:
Sidearm delivery, both long- and short-arm
Crossfire (which I seemed to be using a lot)
Curve ball, which came attached to my sidearm motion
Slider—my strikeout pitch
Knuckle-curve (I think Mike Mussina picked his up the same way I did)
Palm ball
Circle change
"Slip” pitch—a slider thrown with a knuckleball grip
Slow curve
Thw “whoops” pitch—a fast ball, 81 MPH, which I never realized I had until one day when I was warming up—and for a finesse pitcher, that IS a fast ball
Not to mention that Lopat told me once that just about any pitch I had could be turned into a changeup.
And I had the control and command to go with all of this, which pleased me very much. It all made up for the fact that I was no Bob Gibson or anybody like that.