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Are Ground Balls Grounding Astros' Hitters? Will They Ever Take Off?

OK, it's been a tough Astros' season so far.  Take the Astros' offense....Please!  (With apologies to Henny Youngman fans.)

Given the Astros' offensive futility, we can start looking for some statistical reasons.'s Zachary Levine brought up the issue of Astros' hitters' groundball-ways.  That's also a batting characteristic I have been thinking about---particularly with respect to Hunter Pence.  Levine's premise is that some of the main Astros' hitters are hitting ground balls at a higher rate than they have in the past.  As he correctly points out the slugging percent on ground balls is much lower than it is for fly balls, and, of course, line drives.  This is pretty obvious when you think about it.  You can't hit a home run unless you hit the ball in the air.  And it's fairly infrequent that a ground ball turns into a triple or double.

As noted in this article, the average ground ball produces -0.1 runs less than the average outcome of a plate appearance.  An earlier Hardball Times study performed a regression analysis on ground ball / fly ball rates and succinctly concluded:

In general, the more that teams hit the ball on the ground, the less runs they score.

So, where do the Astros rank in ground balls.  A common ratio used for such rankings is "Ground Ball / Fly Ball Ratio."  A higher ratio obviously means that a team's hitters are ground ball heavy. The Astros had the highest GB/Fly ratio in the major leagues in 2009 and continue to lead the major leagues in GB/Fly ratio.  However, the Astros ratio so far is higher than 2009, and the Astros have lengthened their lead over the nearest teams by a considerable margin.

GB / Fly Ratio and MLB Rank


Astros 0.93  (1st)

NY Mets 0.90 (2d)


Astros 1.12 (1st)

Nationals 0.95 (2d)

The Astros' GB/Fly Ball ranking goes a long way in explaining why the Astros rank last in the major leagues in percentage of hits which are extra base hits (26%).

Levine's article compared certain Astros' hitters' 2010 ground ball ratio to their career ratio.  And I'll re-print some of the more interesting individuals from his table:

Player 2010 GB % Career GB %
Michael Bourn 65.2% 57.4%
Hunter Pence 65.1% 52.8%
Tommy Manzella 64.6% 65.3%
Lance Berkman 54.5% 42.3%

I should mention that Manzella's "career GB%" is somewhat misleading.  Manzella only had five MLB plate appearances in 2009.  A better gauge of his career percentage probably comes from his minor league career, which produced a 55.3% ground ball rate.

The average major league ground ball rate is 44%.  Three Astros hitters, above, have ground ball rates above 60%, which is very high. Last year, the Cardinals' Skip Schumaker had the highest ground ball rate among qualified NL hitters, at 61%.  The next highest was Luis Castillo of the Mets at 58.6%.  A speedy runner like Bourn isn't hurt too much by the high ground ball rate, because he will beat out many infield hits and rarely hits home runs.  Players who are the fastest down the first base line, like Bourn and Ichiro, can turn ground balls to their advantage.  Neither Manzella or Pence are in the Bourn-Ichiro class of runners; although both players are ground ball oriented hitters, their current rate nearly eliminates their slugging ability.

Berkman's higher than normal ground ball rate most likely can be ignored--for now--because the sample size on his hitting is quite small.  Ground ball rates are normally very stable for individual players.  That is to say, a player's previous ground ball rate is the best predictor of his current ground ball rate.  We probably can expect regression to mean of Astros' hitters individual ground ball rates.  As a result, it is likely that the Astros' ground ball rate will decline in the future, and although the rate probably will be significantly above average, some relief, in the form of more extra base hits may follow.

Although ground balls produce less slugging than fly balls and line drives, the ground ball will produce a higher batting average than fly balls.  (Line drives are best for both slugging and batting average, as you are probably aware.)  The major league batting averages by type of  ball are shown below:

Batting Average on Balls In Play

Ground Balls .260

Fly Balls .170

Line Drives .710

One might think that the Astros' No. 1 rank in grounder-to-flies would lead to a decent batting average, since that is the advantage that ground ball hitting holds over hitting fly balls.  But that's not the case.  The Astros .227 batting average is third worst in the major leagues. One reason for this is that the Astros rank dead last in line drive rate.  It's also possible that the Astros have been unlucky on their ground balls; as a group, Astros' hitters are only hitting .218 on ground balls   which suggests some bad luck, with balls finding gloves instead of holes.  The Astros also have faced more ground ball pitchers than any other type of pitcher, and they have a worse batting average versus groundballers than fly ball pitchers so far, which seems like an odd result.

Hunter Pence's Ground Ball Rate

Hunter Pence's floundering offense has been of great concern to Astros' fans.  Considering Pence's very high ground ball rate--over 65%--it seems likely that Pence's offensive woes are asociated with the extreme ground ball hitting.

Pence normally has a ground ball rate well above average, usually just over 50%.  Pence has been able to maintain a decent amount of power, despite the ground ball rates.  Although that level of ground ball rate is unusual for a power hitter, a handful of sluggers will exhibit ground ball tendencies.  Derek Jeter (57%), Magglio Ordonez (51%), Joe Mauer (47.8%), Miguel Tejada (49.2%), and Adam LaRoche (48.5%) are other examples of power hitters who have high ground ball rates.  However, it seems doubtful that Pence could maintain a power hitting profile with a 65% ground ball rate.  Presumably, Pence's ground ball rate will decline in the direction of his career rate.

Hunter Pence's current batting average on ground balls is very low.  According to Bill James Online, Pence's batting average on ground balls is .224.  Not only is this low compared to the .260 average for major leaguers, Pence's batting average is stunningly low compared to his normal ground ball hitting.  As evidenced in this article, Pence's batting average on ground balls was among the top 20 highest in the majors in 2007 and 2008 (.340 and .330).  His batting average on ground balls declined to .280 last year, but that was still well above average.   Pence's 2010 BABIP for both fly balls (.105) and line drives (.600) is lower than league average too.  Is it possible that Pence is experiencing bad luck across all types of batted balls?  Possibly. Or maybe he just isn't hitting any of the batted balls as hard as usual.  Conventional saber wisdom would tell us that Pence's sagging BABIP is just misfortune which will turn around in the future. Let's hope that is the case.

The Bill James data also allows us to examine the BABIP on the direction of ground balls.

Pence 2010 Ground Ball Batting Averages

Pulled balls .181

Up the middle .240

Opposite Field .273

The higher batting average on opposite field and up the middle batted balls isn't surprising.  As a general rule opposite field hitting produces higher batting averages on ground balls.  The Bill James data also shows that Pence has been pulling a lower percentage of ground balls this season.  That isn't what I would have guessed, but perhaps those bouncers to shortstop this season are seared on my fan's mind.  It's unclear whether Pence is consciously trying to go the other way and up the middle more often, or whether this reflects a possible late bat.  The former would reflect well on his adjustment process; the latter would not be a good sign.

Furthermore, none of Pence's ground ball hits this season has produced an extra base hit.  The comparison of extra base hit rates for ground balls below shows that he is falling behind previous years.

Extra Base Hit Rates for Ground Balls

2010   0%

2009  4%

2008  7%

2007  15%

This could just be random variation; the sample sizes aren't huge with splits of this nature.  However, one might speculate that Pence just hasn't hit the ground balls as hard so far this season.  Hopefully, this trend reverses, and Pence parks a few balls in the Crawford Boxes in the near future.