Ground Balls and Extreme Splits: How Fastball Location Affects Ground Ball Rate and Explains the Case of Chris Capuano

A heat map showing the areas where a right-handed pitcher's two-seam fastball is better at getting ground balls against right-handed batters than left-handed batters. For an explanation, read on after the jump.




On last Thursday, Dave Allen wrote a post on fangraphs noting the odd ground ball splits of Chris Capuano.  Capuano, despite not having an odd fastball (it's a two-seam fastball with good tailing action but without any sink), is a strong sinkerballer against same-handed batters (left handed batters) but is a clear fly ball pitcher against opposite-handed batters (right-handed batters).  The split came from Capuano's fastball, but Allen could not identify WHY a player, throwing the same pitch to both types of batters would have such different Ground Ball splits.  

If you recall, I talked about one type of pitch, the cutter, which demonstrates extreme ground ball splits at times in a previous column.  But Capuano doesn't throw a cutter...he throws a two-seamer, a type of pitch sometimes called a sinker (one wouldn't call Capuano's pitch a sinker).  And Capuano isn't the only pitcher like this: Both Mike Pelfrey and Ubaldo Jimenez also show extreme ground ball splits despite throwing two-seamers.  But we don't think of sinkerballers as having extreme splits! So what's going on here?

After the Jump, I'll take a look and try to see what's responsible for these odd ground ball splits:

To take a look at this, I queried my database to find all the pitches that fit a broad definition of a two-seam fastball: a pitch with good to great amounts of tail in on same-handed batters and a little more sink than your typical four-seam fastball.  I've almost certainly missed some two-seam fastballs with this definition, but I've collected the most common variation. It should be noted that since I've excluded some two-seam fastballs without any sink at all (that is, those that have similar vertical spin deflection to a four-seam fastball), the GB% numbers below will seem a little high.

First lets take a look at the GB and Swinging Strike splits of these pitches:

Pitcher Handedness
Batter Handedness
GB% Swinging Strike Rate
R
R 57.3% 5.78%
R L 48.8% 4.60%
L L 61.3%
7.38%
L R 49.6%
4.77%

Table 1:  A look at the Ground Ball and Swinging Strike Splits of two-seam fastballs.  Note that the GB% is high because I've excluded two-seamers without at least a little sink, but the table's point should be clear. 

As you can see from Table 1, two-seam fastballs are better at getting BOTH ground balls AND swinging strikes against same-handed batters.  So, if a pitcher uses a two-seam fastball often against both right and left-handed batters, we would expect to see some impact on his split.  Yet, this doesn't completely answer our question; after all, quite a few sinkerballers (Derek Lowe, Joel Pineiro, etc.) manage to get a good amount of ground balls against both same and opposite-handed hitters.  But if this table was to be believed, every sinkerballer should have a problem with opposite-handed batters. 

So lets take a look at WHERE two-seam fastballs get ground balls against right and left handed batters.  Figures 1 and 2 below are heat maps that show the ground ball rate of a right-handed pitcher against left and right handed batters in each part of the strike zone: 

Two_seam_same_and_opposite_gb_rates_mediumFigures 2 and 3: Heat Maps showing ground ball rates all over the strike zone for two-seam fastballs from Right-Handed Pitchers against Right (Same) Handed Hitters and Left (Opposite) Handed Hitters. The darker the shade of black, the higher the ground ball rate of a pitch in that area. The black rectangle represents the strike zone.

This is more informative.  If you really want to get ground balls with a two-seam fastball, you should aim not just low in the strike zone, but on the outside part of the strike zone as well.  This is true against both left and right-handed batters, and is also true for left-handed pitchers, though the heat maps above don't show that.  Note that on figures 2 and 3, the areas with good GB Rates are far smaller against opposite handed batters than same-handed batters....a pitcher can get ground balls against each, but his margin of error for doing so appears to be smaller. 

Figure 4 below shows the difference between the two heat maps more clearly, by showing where in the strike zone is a two-seamer more effective against same-handed batters in getting  ground balls rates:

Two-seamdifferences_medium
Figure 4:  A heat map showing the areas in which a right-hand pitcher's two seam fastball is better at getting a ground ball against same-handed batters than opposite-handed batters.  Red areas are better against RHBs, Blue areas are better against LHBs, and gray-ish areas are basically neutral.  

This of course just shows more clearly what we saw from above:  two-seam fastballs are better in almost the entire strike zone, especially in the middle of the zone, at getting ground balls against same-handed batters.  The only exception is really in the outside and low corner.  Thus if a pitcher always aimed his two-seam fastball in the same part of the strike zone, such as say away against same-handed batters but inside on opposite handed batters, he would come away with extreme ground ball splits. 

Figure 5 below just shows this same effect above once again in another form:

Other_way_of_looking_at_gbs_mediumFigure 5: A chart showing how ground ball rates for two-seam fastballs of right-hand pitchers are affected by where the pitch is thrown in the strike zone.  The Blue line shows the ground ball rate of two-seam fastballs thrown against right-handed batters, while the red line shows the rate against left-handed batters.  Yes the ground ball rates are high, but once again that's because of how I extracted the two-seamers from the data. 

Figure 5 just reinforces our point....to get a ground ball with a two-seam fastball, you should throw away.  If you throw anywhere but away to opposite-handed batters, you're going to find yourself with an extreme ground ball split. 

Returning to Chris Capuano and others:

So, does this explain Chris Capuano?  Well let's see.  First of all, we have to remember that Capuano is a LEFT handed pitcher, so he's naturally going to get better GB rates against left-handed hitters.  And second, lets take a look at Figures 6 and 7, which show the locations where Capuano placed his fastball in 2010:

Capuano_pitches_mediumFigure 6 and 7: The locations where Chris Capuano threw his fastball to left and right handed batters in 2010.  The Black Square represents the strike zone.  The graphs are read from a catcher's point of view: negative numbers are away from left-handed batters and in on right-handed batters; positive numbers are inside on left-handed batters and away from right-handed batters. 

These graphs seem to perfectly explain Capuano's extreme splits:  against left-handed batters, he clearly aims away, making the pitch good at getting ground balls.  But against right-handed batters, Capuano throws in much the same location, which is INSIDE or MIDDLE-IN on these batters, not outside.  This is what causes his ground ball rate against RHBs to be so low. So our look at the ground ball-getting ability of two-seam fastballs in different areas of the strike zone would seem to explain the "odd" splits of Chris Capuano...perfectly.

Conclusion: 

Location would also seem to explain Mike Pelfrey's crazy ground ball splits, just like Capuano.  However, location is not an explanation for ALL ground ball splits.  For example, Ubaldo Jimenez had extreme ground ball splits in 2010, when his splits were not that extreme in 2008 or 2009.  However, Jimenez's two-seam fastball was aimed MORE outside against left-handed batters in 2010...which we'd figure would result in getting more ground balls this year.  But the opposite occurred.  So obviously, this isn't a perfect explanation for ground ball splits, and there will be exceptional cases.

But in general, an extreme ground ball split can often be explained simply in that the pitcher isn't aiming away against opposite-handed batters and frequently this is because the pitcher is aiming the fastball in the same place regardless of batter handedness.  If the pitcher relies upon getting ground balls...this could be a mistake.

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