January 11, 2010

Checking the Numbers

Side Effects on Pitchers' Hitting

by Russell A. Carleton and Eric Seidman

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Let's play myth-busters, shall we?

Two outs. Bottom of the fourth inning at Wrigley in a 2-2 tie game. Strolling to the plate for the Cubs is Carlos Zambrano. He's a good hitter-for a pitcher-with a lifetime .236/.243/.396 triple-slash line and 20 career home runs. In the American League, he'd be on the bench right now with a jacket draped over his right arm, but since this is the senior circuit, he's out there hacking away.

Somewhere in the broadcast booth, an announcer tells the Cubs faithful gathered around their radios that, "The tough part about the pitcher batting is that after a close play like that, where you have to run, it's got to affect him in the next inning."

Really?

The way that broadcasters usually speak, the implication is usually that the pitcher is likely to fall apart in the next inning. If he gives up three runs, they might blame it on his having to bat the inning before. Is this true? Is a pitcher really more likely to falter after batting? Let's take a look at what the data actually says. Start with a database of everything that happened in a National League park during the Oh-O's (that would be the decade that ended a week and a half ago.) Next, figure out if the pitcher on the mound batted in the previous half-inning or not. Simple so far.

It's tempting to say, "OK, show me an aggregated pitching line split by that factor." The problem is that there are some hidden confounds that could influence those numbers. Consider for a moment two factors that no doubt influence a pitcher's performance: his pitch count and the quality of the opposing batters. Why might these be confounds? A pitcher whose pitch count is up is more likely to be pinch-hit for when his turn comes up again, meaning that we are less likely to get to see him with a high pitch count and having batted the inning before. We also need to account for the fact that, particularly in a close game, a manager may allow his pitcher to bat if he knows that the bottom of the other team's lineup is coming up, but not the heart of the order. If the middle of the order is coming up, it's better to send out a fresh reliever, and if the pitcher's not going back out, it's better to send up a pinch-hitter.

Warning: Gory details. Viewer discretion is advised.

So, to control for these, let's use a trick more fully explained elsewhere, that uses a binary logit regression to model the probability that a given plate appearance will end in a specific outcome (say, a strikeout), while controlling for various other factors. It first controls for the relative strengths of the batter and pitcher, using the odds ratio method. Because binary logit works by modeling the natural log of the odds ratio, the natural log of the expected odds ratio of the outcome between this batter and this pitcher was taken, out of a pool consisting only of plate appearances in which a batter with 250+ PA in the relevant season faced a pitcher with 250+ batters faced.

In this particular case, the pitcher's pitch count and whether or not he and the batter were of the same hand were both controlled. The dichotomous variable of whether the pitcher had to bat in the half-inning before was then factored in which, after everything else has been controlled, is the variable most interesting to testing this theory.

This type of analysis requires that we make a few assumptions. We assumed that a league-average pitcher was facing a league-average hitter. You can plug in any numbers you want, but you have to plug something in, and league-average makes the most sense of anything. We assumed that the pitcher had thrown 25 pitches (there's no particular reason for that number, we just have to put something in). Numbers were then run for the eight major outcomes of a plate appearance: walk, strikeout, single, double/triple, HR, HBP, reach on an error, and out in play.

So, was there a significant effect? Yes. A minuscule one.

The probabilities of the plate appearance ending in a strikeout went down by a matter of a few hundredths of a percentage point. Prorated out to 700 plate appearances, the effect was three strikeouts lost. Most of those percentage points seemed to go into the outs-in-play bin (about 2.5 of those strikeouts). That's assuming that a pitcher had to pitch after having just batted all the time. There was also an even smaller effect in which the rate of singles went down and the rate of extra-base hits went up slightly. It appears that a pitcher does become a little bit easier to hit and to hit hard. However, the scale of these effects was so small as to be negligible to any decision-making process. Having to bat does not turn Carlos Zambrano into (Russell's eleventh-cousin-once-removed) Celine Dion. (That's true. Would we make something like that up?)

Just to make sure all T's were crossed, a few variations on this method were applied. What if we only looked at situations where the pitcher had made contact with the ball? What about situations in which we knew he had to do some running because he got on base via a hit? Did it make a difference if he was the last batter in the inning? It turns out that the answer to each was an overwhelming "no." The effects on game outcomes were still significant, but also very, very small.

PITCHf/x Checks In

Thus far, our efforts have focused on the results: Does performance data change after pitchers step to the dish relative to when they get to spend a half-inning munching on sunflower seeds and warming their throwing arm? From a technical standpoint, the outputs indicate that a delta does exist but is lacking in clinical significance despite its statistical significance-the differences are real, but matter very little. Shifting to the inputs drawing these outputs, what does PITCHf/x data have to say? We can theorize that the underlying pitch data should appear similar in both sets of data given the similar results. Using data from 2008-09 and across all pitchers with at least 30 plate appearances, four different tables were built: one including pitch data after innings in which they batted, another with pitch data in innings after not only batting but running as well, and the respective control groups-the pitch data in the other innings.

The rationale behind investigating the base-running aspect under this lens involves the idea of fatigue; while batting could certainly make a difference in the levels of energy and effectiveness of the pitcher, it makes even more sense that a pitcher forced to stay on the bases or hustle around the diamond might lose some energy and effectiveness. Looking at four-seam fastballs, curves, sliders, and changeups, the tables below house pitch percentages, velocities and both movement components. First, the batting vs. non-batting results:

Batting Results    %    velo     pfx     pfz
Fastball         56.2  90.47    5.89    8.74
Curveball        12.1  75.06    5.27   -5.69
Slider           16.7  83.31    2.69    2.55
Changeup         14.8  81.91    6.64    5.24

Non-Batting        %    velo     pfx     pfz
Fastball         58.8  90.58    5.95    8.84
Curveball        10.8  75.12    5.16   -5.58
Slider           16.0  83.35    2.68    2.62
Changeup         14.2  82.01    6.71    5.47

Holding aggregated analysis until the end, here is the running vs. non-running results:

Running            %    velo     pfx     pfz
Fastball         56.6  90.51    5.79    8.78
Curveball        11.9  75.11    5.39   -5.37
Slider           16.3  83.42    2.75    2.51
Changeup         15.0  81.94    6.55    5.18

Non-Running        %    velo     pfx     pfz
Fastball         58.3  90.56    5.94    8.82
Curveball        11.0  75.11    5.17   -5.62
Slider           16.2  83.34    2.68    2.61
Changeup         14.3  81.99    6.71    5.43

What do we see here? For starters, pitchers throw a lower percentage of fastballs after batting the half-inning prior, which is counterintuitive in the sense that it suggests pitchers vary their selections more when supposedly under more physical duress. The percentage shift is extremely small, however, made up by an increase in curveballs, with then numbers of sliders and changeups barely changing. Again, the clinical significance of the delta here is missing. After being on base, a similar drop in the heater rate is evident, with the differences accounted for by ever-so-slight upticks in curves and changeups. From a pitch selection standpoint, nothing here stands out for even a careful observer to spot. The idea of there being any fatigue evident might point towards more fastballs in innings after batting or running; here, we get the insignificant opposite of that expectation.

Moving on to velocity, a larger delta for fastballs is observed in the batting category than in that where baserunning's an additional part of the pitcher's duties, but how important is a drop of 0.11 miles per hour? Hitters may be well versed in identifying the tiniest of tells, but it's far-fetched to suggest that Craig Counsell knows a pitch is thrown 90.27 mph instead of 90.38 mph. Then again, while he and others might be able to make this distinction, the bottom line remains that we do not yet know how hitters react and respond to such situations, or how their perceptions are affected by shifts of various magnitudes. The other three pitches experience even less of a change in velocity, registering reliably similar radar gun readings, though these off-speed offerings are not known for velocity and are more prone to changes in movement.

Movement is tricky to evaluate because a pitch is built upon both vertical and horizontal movement, yet the interaction is tough to quantify, leading to isolated analyses of both horizontal and vertical results. Looking at the fastballs, the change in movement occurs on both fronts, with a 0.05-inch drop horizontally and a 0.10-inch drop vertically. Alone, neither of these seems to matter much, but taken together the fastballs are thrown with less overall movement after batting. After running the bases, however, the shifts switch places, with a minuscule drop in vertical movement, but 0.15 inches of horizontal movement lost. This raises an interesting question for another day, in how a drop of 0.05 vertical and 0.10 horizontal inches compares to losing 0.15 horizontal and 0.05 vertical inches.

In both scenarios sliders feature deltas similar to those of fastballs, where the individual component changes do not seem very different but, taken together, can alter the shape of a pitch more than we think. The more interesting movement alterations occur with changeups in both groups and curveballs after running. The numbers speak for themselves: changeups are thrown with considerably less movement after batting or running, while curveballs after running move more horizontally than vertically relative to not batting or running at all.

While pitch selection, velocity, and even release points remain unchanged for the most part after hitting or running, the signs of fatigue surface in the form of movement, one of the areas of PITCHf/x data that remains relatively unexplored. We know about movement in general terms, in that decreases are considered suboptimal, but we do not know about the ramifications of a quarter-inch drop in one of the components. These results make sense when used in conjunction to prior research on similar subjects, which conclude that fatigue surfaces more in the movement of pitcher's offerings than in their velocity or any other departments.

Wrapping Up

Having to bat or run in the top of the inning does change what we can expect from a pitcher in the bottom of the inning-slightly. Though the changes in movement could hold clinical significance in any portion of this study, it did not result in a huge downturn in performance, lending credence to the idea that these movement shifts, however different relative to the other inputs, might matter very little. Broadcasters who say that there will be an effect are correct, but when they imply that it will be a massive shift, they're wrong. A pitcher might be a bit more tired in such circumstances, but he is unlikely to start throwing three miles per hour slower or from a much lower release point, just as he is unlikely to suddenly serve up gopherballs as if he were on Eric Milton-autopilot.

Myth busted, for now.

Russell A. Carleton, the writer formerly known as 'Pizza Cutter,' is a contributor to Baseball Prospectus. He can be reached here.

Russell A. Carleton is an author of Baseball Prospectus. Follow @pizzacutter4
Click here to see Russell's other articles. You can contact Russell by clicking here
Eric Seidman is an author of Baseball Prospectus. 
Click here to see Eric's other articles. You can contact Eric by clicking here