You're ahead in the count 0-2. You are a typical high school pitcher that has somewhat decent command of 2 pitches-fastball & curve. Let's say that you are a RHP working to a RHH. What do you do next? Here are a few suggestions:
First of all, I hope that your catcher has been trained properly. As a pitching coach, I would not want any pitch thrown above the knees in this situation (the exception might be when you have an unbelievable, blazing fastball that you haven't just shown him). So, your target (the catcher's glove) should be held below the hitter's knees. Remember that since you are on a mound, you are substantially "taller" than the hitter and you are throwing on a downward plane. Since the ball is moving downward as it's approaching the target (either a fastball or curve) a pitch that crosses the plate knee-high will hit the catcher's glove below the knees. Your catcher can give the sign with his feet close together and with his body upright but after the sign is given, he should spread his feet apart and bend forward at the waist to make himself as "short" as possible. If the glove is held low and he makes himself short, you, as the pitcher, will see a very small/short image that will help you get the ball DOWN.
OK. You've decided to pitch down because a pitch at or below the knees is usually the most difficult for a batter to hit well. Next, you have to decide whether to throw the fastball or the hook. If you got him out on an 0-2 pitch earlier in the game, he will be looking for that pitch again so just give him the other one. Also, if you threw an 0-2 pitch that worked to the previous hitter in the same inning (or even two hitters earlier) give him the other pitch. Otherwise, why not go with the fastball since it's probably your most accurate pitch.
Let's say that you choose a fastball-down. You are either going to come inside or go outside (you wouldn't groove one on 0-2, even if it's low). If the hitter is really crowding the plate or if he leans out over the plate while swinging, your catcher should set up on the inside corner. The hitter shouldn't even be able to touch that! If the hitter positions himself at a normal distance, the glove should be at least eight inches (maybe more) off the corner. If the batter reaches out and fouls off the outside pitch, you could consider coming down-and-in on the next pitch. Just make sure that it's "in" enough if he's not crowding the plate.
Let's say that you decided to go with the hook. In this situation the hitter probably wouldn't be surprised to see a curve. For this reason it should not be thrown for a strike. Normally, the only time a curve should be thrown for a strike is on fastball counts when the hitter is sure that he'll get a fastball. On an 0-2 count the curve should be thrown so as to breaklow-and-away.
This is certainly not the only strategy that a "two-pitch-pitcher" can use for this situation but it usually works pretty well for my pitchers. Or you could develop complete command of 3 pitches like Pedro Martinez.
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