The Relationship Between Fielding Effectiveness And Balls In Play

What you see before you is more than a funny looking picture. It is a symbol of my unrelenting devotion to truth, the physical embodiment of some of the data to be revealed in this post, and evidence that I am a Grade A dork. But let’s not focus on that last one. This thing is called a “boxplot,” and I know that because my good friend and occasional commenter told me so after creating it for me. This friend graduated from Vanderbilt with me in 2008, and has gone on to earn two master’s degrees – one in economics, and one in mathematics. He is also the person I turn to when I have a hypothesis, a ton of sports-related data in a spreadsheet, and not a blasted clue about what to do with it. So, R. Thomas, this boxplot’s for you.

Back to sports. If you are a baseball fan and you watch baseball games, I’m willing to wager my considerable life savings that you’ve heard an analyst talk about the importance of fielders “staying on their toes.” This usually happens when a pitcher is working quickly and accumulating outs fly and ground balls. The analyst will talk about how keeping the fielders involved in plays increases the quality of the defense behind the pitcher, because it prevents fielders from getting distracted, dozing off, or stiffening up due to lack of movement. This saying is, at its core, a variation of the old “practice makes perfect” dictum. If a pitcher pitches in such a way that his defenders stay involved and get into a fielding rhythm, their defense improves. That’s what they say.

Of course, just a small amount of critical thinking reveals some serious holes in this logic. Supposing pitchers do have some control over how and where their pitches are hit (a huge and false supposition), wouldn’t leaning so heavily on their defense yield tired fielders? If pitchers do have this sort of control, shouldn’t they just remove any possibility of an error and try and strike batters out? Wouldn’t the increased number of balls in play create more chances for hits and fielding errors? There are a ton of problems with the idea that fielders field better when under constant fire, but that hasn’t stopped it from emerging almost daily during baseball season.

Well, this is me doing my small part to refute this erroneous claim. The first thing I did was acquire the number of balls in play allowed by the pitching staffs of every major league team since 1990. Then I looked up each team’s defensive efficiency, which is the rate at which balls put into play are converted into outs. Lastly, and with the necessary help of my aforementioned friend, I examined the relationship between the two via the correlation function in Excel. The results shed light on the extent to which the two variables (balls in play and defensive efficiency) are related. The closer the number is to +1.0, the more positive the relationship between the two is (if one goes up, the other goes up). The closer the number is to -1.0, the weaker the relationship between the two is (if one goes up, the other goes down). I’m sure this is fascinating, so I hate to tear you away from the riveting inner-workings of statistical functions, but here are the results:

  • 2009: -0.42
  • 2008: -0.59
  • 2007: -0.32
  • 2006: -0.52
  • 2005: -0.56
  • 2004: -0.02
  • 2003: -0.15
  • 2002: 0.11
  • 2001: 0.13
  • 2000: -0.03
  • 1999: -0.11
  • 1998: -0.53
  • 1997: -0.50
  • 1996: -0.36
  • 1995: -0.50
  • 1994: -0.29
  • 1993: -0.53
  • 1992: 0.08
  • 1991: -0.49
  • 1990: -0.20

As you can see, only three (1992, 2001, 2002) of the past 20 seasons reveal some sort of positive relationship between the number of balls in play and defensive efficiency. And in all three cases, the positive correlation is quite weak. On the other hand, the 17 other seasons that I examined reveal a negative relationship between the two variables. With a few exceptions (1999, 2003, 2004), the negative relationship is pretty pronounced. As a result, these numbers suggest fairly strongly that, at least in the last 20 years, defenses labor when more balls are put into play by hitters. This makes a great deal of sense given the very obvious and intuitive problems with the whole “keeping fielders on their toes” idea.

I’m sure this information is completely unsurprising to baseball teams and the (usually) very bright individuals who run them. By no means is this meant to be some sort of breakthrough that organizations can use to construct better teams. Instead, this post is targeted at those who believe (or have got into the habit of saying) that fielders perform better when they are put to regular work. I’ve heard broadcasters say that fielders are more comfortable when they remain active in the game, and I have no doubt that some players truly feel that way. But in the last 20 years, increased fielding activity has in no way boosted teams’ defenses. In fact, the opposite appears to be true.

I guess the key to good defense is just having plain old good fielders.


2 Responses to The Relationship Between Fielding Effectiveness And Balls In Play

  1. R. Thomas says:

    First off, thanks for the shout out. I do have to correct you in saying that I only have one master’s, but hey.

    More importantly, I think there are two things you can do to include the time aspect. You can see if balls in play changes over time, and if defensive efficiency changes over time. I think it would bolster your conclusion here and give you some more opportunities for analysis.

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