Thursday, October 18, 2007

Designated Hitters

I don't know about you, but whenever I picture a designated hitter, it's a thunderfooted, lumbering, home run masher. David Ortiz plays well into the conventional thinking of a quality DH. The thing is, however, not all DH's are home run hitters. In fact, especially on bad teams, many times the DH is just whatever position player on the team needed a day off defensively. To wit, the Tampa Bay Devil Rays this year used 13 different designated hitters, with Greg Norton leading all players with 46 starts.

In order to try and verify the perception of designated hitters as pure mashers, I decided to use the league splits (Example: 2007 Major League splits) at to get data on DH performance since the DH rule was enacted in 1973. Since National League teams don't have to plan a roster spot for the designated hitter, I decided only to look at American League numbers. Since the advent of interleague play, the non-DH numbers are slightly skewed due to pitchers batting, but the effect shouldn't be too drastic.

First, let's look at the traditional, though flawed, measure of batting average to compare designated hitters to the rest of the league:

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Alright, so we can see that traditionally designated hitters hit for a lower average than the rest of their AL counterparts. This seems to support the idea that DH's aim to hit for power rather than average. Note the sharp dropoff in 1985; this isn't the last time we'll note that particular season.

Now let's turn our attention to a hitter's main goal: avoiding outs. On Base Percentage helps us here, as it's a measure of a player's ability to, well, get on base and avoid outs.

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Here we can see that designated hitters generally have been better at getting on base than the rest of the AL. This is especially apparent in the mid-to-late 1990's. Interestingly, for the first decade after the DH rule took effect the players in the DH role did not really distinguish themselves from the rest of the league. This graph also shows the mysterious dip in 1985.

So designated hitters get on base more than the rest of the league. Woohoo. If they really are so good at driving the ball, it should show up in their slugging percentages. Let's take a look:

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So, every year since 1973 has seen slugging percentages by DH at least equal to the rest of the league. In many cases, designated hitters slugged much better than the rest of the league. It's beginning to become repetitive, but the one season the rest of the league caught up to their DH's was...1985! This chart confirms the idea of designated hitters being better than average at mashing the ball. In fact, the last two charts show the overall superiority of players used as DH's at hitting in general. Using OPS, or On Base plus Slugging, a metric giving a quick-and-dirty yet useful approximation of a hitter's value, we can see the value of designated hitters.

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As we can see, and as we gathered from the last two charts, designated hitters have a higher OPS than the rest of the league virtually every season. The only expection, obviously, was 1985. What exactly went on that year, anyway?

Baseball-Reference also has an interesting split statistic called tOPS+. This statistic compares how DH's compare to the numbers for the whole league. Anything over 100 means they were better than the rest of the league in terms of OPS, while anything less than 100 means they were worse. You might say this chart is a re-hashing of the last one, but it gives an impression of the degree to which DH's were better than the rest of the league. Finally, tOPS+ has a pretty simple formula for this chart: 100*((DH_OBP/AL_OBP) + (DH_SLG/AL_SLG) - 1).

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It turns out that ever since roughly 1991 those DH's have been much better than the rest of the league. The expansion year (for the NL) in 1993 saw a dip in DH dominance, but other than that the designated hitters have exceeded 110 every season. Who could have figured that 1985 was the only year since 1973 that DH's were worse than the rest of the league? Anyone?

To recap, we've determined that DH's generally hit for worse average (swinging for the fences?), get on base more (walked because they represent a power threat?), slug better, and put up higher OPS numbers than the rest of the league. If they truly are swinging for the fences because they're home run hitters, might it show up in their strikeout percentage (strikeouts over at bats)? I think it might, but let's appeal to the chart:

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Well, well, well, it turns out these guys are free swingers. While strikeout percentage overall has gone up since 1973, it's gone up faster for designated hitters. For the last dozen years, one out of every five at bats by a designated hitter has been a strikeout (as opposed to two out of eleven for the rest of the league). Pretty neat stuff.

Finally, there's one more statistic that might tell us whether designated hitters are swinging for the fences. I'm referring to home run percentage, or home runs over at bats. This should give us a final clue to the power displayed by designated hitters. Here we go:

(click image to enlarge)

So, perhaps obviously, it turns out that designated hitters do hit home runs at a higher percentage than the rest of the league. Just eyeballing it, it seems as though the HR% for the average DH is 4/3 that of another average position player. That's pretty cool.

I may have just spent a significant amount of time telling the world what it already knew: designated hitters are better hitters than the rest of the American League. It took some time for patience and/or other on-base skills to develop, but the slugging percentage, strikeouts and home runs were always there. If nothing else, I hope this lengthy post brought the fact designated hitters in 1985 suffered a dip in numbers compared to the rest of the league. I'm not really sure why that is, but in hopes someone sees something, I'll list below the batting lines for every player to spend 50 or more games at DH in 1985. Thanks for reading this marathon entry!

Ron Kittle27CHW57.250.305.526.831
Hal McRae39KCR105.264.355.459.814
Jeff Burroughs34TOR74.267.377.433.810
Gorman Thomas34SEA133.215.330.451.781
Don Baylor36NYY140.232.332.432.764
Cliff Johnson37TEX103.264.337.425.762
Larry Sheets25BAL93.262.323.418.741
Mike Easler34BOS130.259.320.411.731
Reggie Jackson39CAL52.196.335.387.722
Roy Smalley32MIN56.244.348.372.720
Ted Simmons35MIL99.265.325.390.715
Dave Kingman36OAK149.233.301.404.705
Andre Thornton35CLE122.235.301.400.701
Jorge Orta34KCR85.263.310.384.694
Al Oliver38TOR59.253.276.376.652
Len Matuszek30TOR52.220.265.319.584

The only thing that struck me as curious was Reggie Jackson's bizarre split as RF/DH (.286/.378/.555 in 325 PA vs. .196/.335/.387 in 206 PA). He spent slightly more time as a designated hitter late in the season but overall his starts are pretty mixed up.

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