Two of the first things you learned about sabermetrics were that batting average is not a very good measure of a hitter, and that fielding percentage is not a very good measure of a fielder. Not all hits are created the same, and extra-base hits cause a lot more damage than singles, which is why we know that slugging is better than batting average at approximating hitting ability. We also know that fielding percentage is a poor measure of defensive skill, because it only considers the balls that a fielder can reach, and therefore does not account for range-being able to get to more balls, all else equal, implies that a fielder is better. Being able to record outs on more balls in play is indicative of better team fielding. That is why the most widely used measure of team defense is Defensive Efficiency, which is effectively one minus your opponents’ BABIP (including errors).

However, there is a fairly obvious disconnect between those two facts: on the one hand, we avoid using batting average to measure a team’s offensive ability, but then we encourage the use of batting average to measure a team’s fielding ability. However, teams frequently guard the lines to avoid doubles late in a game-at the expense of making singles in the hole more likely-and play their outfielders deep to avoid extra-base hits-at the expense of letting singles drop in more frequently. These can be wise tactics in certain situations, since there are times when an extra-base hit would be particularly costly. Sometimes acquiring fielders who make doubles and triples less likely is wise, even if it means not acquiring fielders who can prevent singles. Teams that prevent hits are not necessarily the teams that prevent extra-base hits-and therefore are not necessarily the teams that prevent runs.

For this reason, I am introducing a new statistic we can use to measure team defense: Slugging on Balls in Play. It’s measured exactly how you think it should be: it is simply slugging on all at-bats that do not end in home runs, strikeouts, walks, hit by pitches, or sacrifice bunts, but it counts reaching on errors as singles.

Here are the list of all teams’ 2009 SLGBIP and RBIP (slugging on balls in play, and reaching on balls in play-which I define as batting average including errors), through Saturday’s action:

         SLGBIP          RBIP
Team      Rank   SLGBIP   Rank   RBIP
Mariners   1      .354     2     .289
Dodgers    2      .360     1     .285
Reds       3      .371     4     .297
Giants     4      .371     3     .293
Cubs       5      .372     6     .299
Rangers    6      .374     5     .297
Cardinals  7      .379    11     .305
Yankees    8      .379     7     .302
Padres     9      .380    12     .306
Phillies  10      .381     8     .302
Rays      11      .383     9     .303
Tigers    12      .383    10     .304
Twins     13      .386    15     .309
Angels    14      .391    18     .312
White Sox 15      .392    21     .313
Athletics 16      .394    19     .313
Mets      17      .395    17     .311
D'backs   18      .397    20     .313
Rockies   19      .397    16     .311
Brewers   20      .397    13     .307
Indians   21      .400    25     .318
Marlins   22      .402    26     .317
Astros    23      .406    27     .320
Pirates   24      .406    14     .308
Red Sox   25      .406    29     .320
Braves    26      .406    23     .315
Blue Jays 27      .406    24     .318
Royals    28      .406    30     .324
Orioles   29      .410    28     .320
Nationals 30      .411    22     .315

I have also included each teams’ rank at preventing slugging on balls in play, and at preventing hits on balls in play. Perhaps with an eye towards the example set by the Rays’ worst-to-first shakeup in part through their defensive improvement in 2008, the Mariners are one the latest teams to stress defense as a means to improvement. In particular, they’ve stressed outfield defense, and after putting together an excellent defensive outfield, they lead the league in SLGBIP. Another interesting example is the Pirates, who are 14th at getting outs on balls in play, not bad, but they are 25th at slugging on balls in play, at .406. As a result, their ERA is a little bit higher than their FIP.

Note that I have used FIP, fielding-independent pitching, which is a statistic that approximates what pitchers’ ERA should be based on their home-run, walk, and strikeout rates. As has been discussed previously, FIP is not as stable a statistic as xFIP or QERA, but it is what we are looking for here because we’re looking for a statistic that accounts for the fact that home runs have been hit, and delivers an expected ERA conditional on the number of home runs, strikeouts, walks, and hit batsmen occurred, assuming average defense and average luck. Much of the difference between ERA and FIP is therefore team defense. A statistic like xFIP or QERA might be better at measuring a pitchers’ run prevention, but the difference between realized FIP and ERA will be highly correlated with defensive abilities.

Looking back at 2008, we see the following rankings for SLGBIP:

        SLGBIP           RBIP
Team     Rank   SLGBIP    Rank    BIP
Brewers    1     .372      7     .302
Mets       2     .373      6     .302
Rays       3     .373      1     .290
Padres     4     .376      9     .304
Blue Jays  5     .378      3     .296
Red Sox    6     .378      5     .301
Athletics  7     .381      4     .300
Cubs       8     .382      2     .295
Dodgers    9     .383     16     .309
Angels    10     .383     15     .308
Orioles   11     .383     18     .312
Marlins   12     .385     13     .307
Phillies  13     .386     11     .305
Indians   14     .388     22     .314
Twins     15     .389     19     .313
Astros    16     .389      8     .302
Nationals 17     .390     14     .311
Royals    18     .393     17     .310
D'backs   19     .394     21     .314
Cardinals 20     .396     10     .305
Yankees   21     .396     25     .318
White Sox 22     .399     20     .314
Braves    23     .400     12     .306
Giants    24     .401     23     .315
Tigers    25     .403     24     .315
Mariners  26     .405     26     .318
Reds      27     .415     29     .327
Pirates   28     .416     28     .325
Rockies   29     .416     27     .322
Rangers   30     .421     30     .330

Perhaps the most interesting result here is that Milwaukee tops the list, even though they were only seventh in getting outs on balls in play. However, they led the league in the difference between their ERA and their FIP. This was partly due to Mike Cameron, who had a UZR of 11.3 in just 119 games. Surprising nobody, the Rays were also particularly good at defense in 2008; while going from worst to first in Defensive Efficiency, they were also very nearly the best in SLGBIP too, thanks to superb outfield defense.

The Orioles are also an interesting team. They were 18th in the league in getting outs on balls in play, but were 11th at keeping their club SLGBIP down, so their ERA and FIP were nearly identical. Something particularly interesting about the O’s is that they had such a difference between their infield and outfield defense: their infield defense had a combined UZR of -32.2, but their outfield defense had a combined UZR of +38.9. Nick Markakis, Jay Payton, Adam Jones, and Luke Scott combined to help them prevent a lot of extra-base hits, as the team gave up twelve fewer doubles to center than the league average, and four fewer triples to center than the league average. They also gave up ten fewer doubles to right than league average, and about 1.5 fewer triples than average. Melvin Mora at third base and the handful of players manning shortstop combined to allow a lot of hits on balls in play-but many were singles.

Let’s have a look at the SLGBIP tables for 2007:

         SLGBIP           RBIP
Team      Rank   SLGBIP    Rank    BIP
Blue Jays   1     .363      1     .294
Padres      2     .375      4     .297
Red Sox     3     .375      3     .296
Cubs        4     .376      2     .295
Nationals   5     .378      6     .301
Braves      6     .381      7     .302
Mets        7     .382      5     .299
Rockies     8     .387      8     .303
Orioles     9     .388     20     .316
Cardinals  10     .389      9     .303
Dodgers    11     .390     19     .315
Athletics  12     .391     11     .308
Indians    13     .392     18     .315
D'backs    14     .393     14     .310
Tigers     15     .393     12     .308
Twins      16     .394     17     .314
Yankees    17     .395     15     .310
Giants     18     .397     10     .307
Rangers    19     .399     22     .318
White Sox  20     .400     23     .319
Phillies   21     .401     16     .313
Astros     22     .402     13     .309
Angels     23     .402     24     .320
Brewers    24     .410     26     .325
Pirates    25     .412     28     .330
Reds       26     .412     25     .325
Royals     27     .414     21     .317
Mariners   28     .415     27     .327
Marlins    29     .418     29     .337
Rays       30     .437     30     .343

Toronto led the league in SLGBIP and Defensive Efficiency in 2007. Interestingly, although they stayed near the top of the league in 2008, they fell quickly towards the bottom in 2009.

Looking at 2007-09 together, we can see some patterns emerge. Preventing hits on balls in play seems to be largely related to infield defense, but preventing extra-base hits on balls in play is largely related to outfield defense. The correlation between UZR of infielders and reaching on balls in play was .39, but the correlation between UZR of outfielders and reaching on balls in play was slightly lower at .36. The correlation of UZR of infielders and SLGBIP was .22, however, and the correlation of UZR of outfielders and SLGBIP was .40. It certainly seems that the Mariners’ 2009 charge towards improving outfield defense is the way to go.

Of course, the correlation between UZR of a team’s infielders combined from year-to-year is much stronger than that of outfielders at the team level (.34 versus .10), so it may be tougher to help your team consistently prevent those extra-base hits. But what we have learned here is that looking at slugging on balls in play is important, and is a helpful additional way to look at team defense. As defensive metrics get more and more refined at the individual player level, it remains true that these are often difficult to truly interpret, and separating the effect of different players is still a challenging endeavor. These metrics at the team-wide level remain far more reliable and important to use as a benchmark, and slugging on balls in play is another way to measure it.

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Do you have any explanation or theories on why the Orioles, who were 9th in SLGBIP in 2007, and 11th in 2008 have fallen all the way to 29th in 2009? Jones has still been the predominant center fielder, and Markakis is still in right. Does the change in left field really make that much of a difference? To what degree do team numbers stay consistent from year to year? We know, for instance, that measures of "clutch hitting" such as BA with RISP can be generated, but are not considered to measure an "ability" because they fluctuate so much from year to year. To what degree is this pitching rather than defense? For example, one would assume that a ground ball pitcher would have a lower SLGBIP than a fly ball pitcher. These are interesting concepts. I look forward to greater refinement.
I'll look into this. I tried to do some tests and it seemed like the correlation of BABIP and SLGBIP were similar, but I'll try and dig up a larger sample to check.
How do park effects play into this analysis? When evaluating hitters/pitchers there is a constant emphasis on adjusting for parks, but typically when discussing defensive metrics the park is generally overlooked (even though, frequently it appears that it is just an inverse correlation). PADE adjusts for this (but on something like SLGBIP, it feels that the absolute numbers have a lot to do with the home demensions rather than the defensive talent).
yes - my question exactly. Some parks are small and just don't allow many doubles and triples. Others have huge gaps and allow a lot of doubles and triples, and it doesn't seem like that's due to poor defense. Thoughts?
I see that the variance in the SLG_BIP are around 15%. Park effects could thus significantly change the rankings. While my Padres are no slouches defensively, I suspect this is largely due to Petco.
Absolutely, and I'm planning on getting to that. It was a bit too much to chew off for this article, but it's definitely my plan to look at park effects. Thanks for pointing this out.
SLG on balls iin play? It's so simple, I can't believe I didn't wonder about this sooner. Thanks a lot for this piece!
Oh yeah, I agree w/ this too! Great idea. I'm very happy when a new stat pops up that is actually useful and EASY TO UNDERSTAND!! :)
Slugging on Balls in Play still isn't really pitching independent; if a team has a staff of groundball pitchers then the defense will give up a lower number over the course of the season even if their defense isn't as good as another team whose pitchers allow tons more flyballs. I have no idea what variance there is between flyballs/line drives/grounders given up by all these teams but it'd be interesting to see how that plays into the statistics as well.
Actually, slugging on balls in play at the team level is lower for flyballs: .236 vs .257 on groundballs. BABIP on groundballs is much higher, .236 vs .138. Although the ISO is much bigger for flyballs, the BABIP difference more than makes up for this. In reality, I guess, this is less biased at the team level than BABIP.
right, doesn't pitching quality matter as well? as in, a worse staff would give up more hard-hit balls to the OF, no?
I'd be real wary of reading too much into team SBIP. Too much effect from park and the pitchers. While pitchers do not have that much control over BABIP, they certainly have more control over doubles and triples. In fact, there is a fairly strong correlation between a pitcher's HR rate and his extra base hit rate. If anyone wants to check, I am going to guess that the best teams in SBIP also had a pitching staff which allowed fewer HR than average, and vice versa for the worst teams in SBIP.
Is there a correlation between a pitcher's HR rate and his extra base hit rate on balls in play or just his overall extra base hit rate? Given the similarities in between SLGBIP on flyballs and SLGBIP on groundballs, and the lack of autocorrelation on line drives, I would guess that maybe this is less true than it seems. Pitchers who give up a lot of doubles and triples probably do give a lot of homeruns-- but mostly because pitchers who give up a lot of homeruns are pitchers who allow a lot of contact in general rather than pitchers who miss bats. The park effects issue is certainly huge, and I'm going to work on improving this for a later article to correct for this. This was just a starting point. Thanks for your comments.