What makes a home run pitch

It’s the bottom of the ninth, and the healthy lead you’ve been holding all game starts to come into jeopardy as you load the bases with an arm that is growing increasingly numb. The pitching coach makes his excruciatingly slow walk to the mound and grunts: “This is your last batter. Closer’s almost ready. I don’t care how you do it, but find a way to keep the ball in the park against this guy and we’ll get you the win.”

So what do you throw? As John Walsh pointed out in a previous article, fastballs generally leave the yard at the highest rate, but is that true for all locations? We often hear about the high “hanging” curveball, or slider, that is supposedly a snap to hit out of the park, and that really high heat is impossible to do anything but pop out. Well just how high is enough to make a difference, and what about throwing an outside pitch that will be harder to pull? This article is going to use PITCHf/x to take a close look at what makes each kind of pitch more likely leave the yard.

First, here’s a look at how home rate is related to height, regardless of the type of pitch. The following graph shows how the percentage of balls in play that went for home runs relates to how high above the ground they were.

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According to PITCHf/x, the average vertical strike zone is about 1.6 to 3.5 feet above the ground. Notice that the first bottom six inches of the strike zone are crucial. Every inch lower that a pitcher can keep the ball at the bottom of the zone makes a big difference, as opposed to the gradual increase through the heart of the vertical zone.

Now we already knew that keeping the ball down was important for just about everything pitching related, but somewhat unexpected is that the most likely place to hit a home run is not right down the middle, but at the extreme upper limit of the zone. However, go just a couple of inches above that and the home run rate drops sharply as players are suddenly unable to get on top of the ball (and then fluctuates wildly because so few balls are put in play).

Now let’s break things down by pitch type:

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One thing to note is that this graph just shows the percentage of each pitch that is hit for a home run at each particular height. That is why the home run rate for curveballs is sometimes higher than that of fastballs, despite more fastballs being hit for home runs overall; relatively few curveballs are thrown up in the zone, but when they are, they are more likely to be hit for a homer than a fastball in the same spot.

I used John Walsh’s method of classifying sinking fastballs (anything less than 6 inches of vertical movement is classified a sinker) because I’m not convinced that even modern technology can tell cut fastballs from sliders and moving-four seamers from sinkers—or that there’s even a clear difference between them. But clearly, fast and sinking is far and away the best way to prevent home runs, at least until the top of the zone where there is very little difference between pitches, anyway. The fastball graph follows almost the same path as the first graph, which makes sense, as about 65 percent of all pitches are fastballs.

The slider clearly is the pitch most dependent on height. If a pitcher can locate a slider right at the knees, even if it is in the strike zone, there is essentially no chance of it leaving the park. But the chance of a home run increases quickly as pitchers leave them higher until just above the belt, where it becomes the easiest pitch to hit out, but then surprisingly falls off towards the top of the zone. I’m don’t know if anyone ever intentionally throws a high slider, but it would be one way to keep the ball in the park (perhaps on shock value alone?).

All in all, we’ve probably confirmed more than we’ve learned in looking at how height affects home runs. Sinkers are very hard to lift, hanging sliders are a pitcher’s nightmare, and keeping the ball down as far as possible pays huge dividends. But very high offspeed pitches aren’t the guaranteed home runs they are usually made out to be, and in fact the low curveball slightly more likely to be driven out of the park despite its huge downward drop on the way to the plate.

Now, let’s see how the horizontal location of a pitch relates to its probability of leaving the yard. Here it is important to split up the handedness of the pitcher and batter, as a slider that ends up low and away follows a completely different trajectory when coming from a lefty than a righty (although it turns out the final results are not as different as you might think).

The following two charts are the same as the previous ones, but looking across the plate from side to side from the catcher’s perspective. They show results for right-handed batters against right-handed and left-handed pitchers, respectively. I’ve only shown the results for right handers because it turns out that, as a group, their results don’t differ significantly from those of lefties.

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And for different handed matchups:

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As you would expect, the matchups that favor the batter result in a higher home rate across the board, but it seems much important where the ball ends up than which side of the mound it was released from. Hitters prefer a pitch slightly inside, which they can pull. They get jammed by pitches too far inside, and then see a steady decrease in their home run power as the ball gets further and further away from them, to the point that a pitch on the very outside corner has almost no chance of being hit out of the yard.

Now here are the same graphs for each pitch type.

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Again, they’re very similar, with only one or two minor differences: While inside changeups and curveballs leave the yard at an extremely high rate when left in the sweet spot (slightly inside), curveballs thrown inside by a lefty to a righty are not hit as well, perhaps resulting in the cliche of the lefty with a big breaking ball.

Also, sinkers don’t seem to be as dangerous when left inside by right-handed pitchers to right-handed hitters situations, but when coming from the other side, they must be kept away to prevent home runs. One possible explanation for this is that since sinkers also tend to tail, they break into the hands when thrown from a right-handed pitcher to a right-handed batter, while from a lefty that pitch will start inside and then come back over the plate.

So what have we learnt from all this?
{exp:list_maker}That if you can spot a pitch on the very corner, be it the very bottom of the zone or right on the outside corner, then there is a miniscule chance that it’s going to leave the yard.
That all pitches left high are home run pitches, not just offspeed ones.
That down and away isn’t many a pitchers bread and butter for no reason, as both are very important to sap home run power. {/exp:list_maker}

But otherwise, there isn’t that much difference between where each type of pitch has to be thrown to avoid disaster, or any secret locations where hitters plain can’t handle them. No matter what a pitcher throws, or from which side, the most important factor to preventing the home run is location, location, location.

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