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Team Defense


“Thou hast set thine house of defence very high.”

– Psalm 91,

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Defense: The Traditional Baseball View

(This discussion assumes you have already read the material available on this site about general baseball statistical-analysis theory.)

Baseball is traditionally held to comprise three elements: pitching, hitting, and defense. In that tradition, the three are further held to be roughly equal in importance. Modern baseball analysis, discussed at length all over this site, has had much to say about batting and pitching performance; but many feel, as analysis pioneer Branch Rickey put it in 1952, that there isn’t much that you can (analytically) say about baseball defense. But that is not so at all.

First off, we know (from the successful games-won formulae) that runs scored and runs allowed are of equal value*, so since runs allowed are a function of pitching and of fielding, clearly batting, pitching, and fielding cannot be of even roughly equal importance: offense must come first—then pitching and fielding can vie for second and third place. But, as we will see, there are profound problems in trying to disentangle pitching from fielding (or vice-versa).

* In truth, offensive runs and defensive runs are not dead exactly equal in value, because improvements in offense (more runs scored) raise the “run environment”, while improvements in defense (fewer runs allowed) decrease the “run environment” (the “run environment” determines the relative importance of runs, because one run tends to mean less when many are being scored and more when few are being scored). But in the realistic range of run scoring in major-league baseball, the difference is essentially negligible. A .500 team that both scores and allows 750 runs but then improves its defense by 50 runs (to allowing only 700) will likely win 86 games; if it instead raises its offense by 50 runs (to score 800), it would likely win…86 games. The exact projected numbers are 86.25 wins from improved defense and 85.92 wins from offense, a “difference” of 0.33 wins that washes out in the rounding off (since one cannot win or lose a fraction of a game). And a 50-run change is a pretty big one. So none of that materially impacts the order of importance.

As to pure fielding, one major problem (as always with analysis) has been a lack of good data. The traditional (that word again) baseball measure—Fielding Percentage—may have been (but one doubts even this) useful in an era when even “major-league” baseball fields were so terrible that errors were common in the best of cases: today it’s flat-out silly.

Only yesterday, or so it seems, the concept of “Range Factor” was introduced in an attempt to make better measure of individual fielders’ abilities. Range Factor in its earliest incarnation was total successful fielding chances (by player by position) per game played; later versions reasonably changed the measure to total successful chances per 9 innings played at a given position (rather than “games”, which could mean anything from 15 innings to 1/3 of an inning).

More recently, we have seen a slew of player-fielding measures, such as “UZR” (“Universal Zone Rating”), many derived from “secret-sauce” undisclosed proprietary techniques (some of which are actually subjective, or at least rely on certain subjective assessments). We will not here explore the problems with such numbers, though they are manifold; rather, we will focus on fielding at the team level.

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Making Team-Level Defense Metrics

A team-fielding metric is not hard to invent, though there are some tricky details. We start by asking ourselves what is the basic job of fielders? Answer: To make an out on every possible play. And what is a “possible” play? There are actually two categories of “possible play”; let’s start with the more obvious, possible plays on batters.

We start with every man who comes to the plate, then subtract out those men whom the fielders can do nothing about: strikeouts, walks (“you can’t defense a walk”), hit batsmen, catcher’s interference, and home runs (in theory some minute fraction of home runs could be caught at the fence by a leap, but the number is very small, and the variation in that number from team to team is negligible).

Stats, Inc. reported (in their Baseball Scoreboard for 1996) that the number of home-run-saving catches in all of major-league baseball for the 1995 season—presumably representative—was all of 64, or about 2 a team a season. Even over a three-season period, no one outfielder made more than 6 such catches, or 2 a season a man (and those in parks with low fences). And we may confidently assume that at an average rate of 2 a year a team, the variation from team to team in ability to stop at-the-fence homers is utterly negligible: those that can be made mostly are made and those that can’t, aren’t.

So the first team-defense metric, which we can (and do) call FEbat (Fielding Efficiency on batters) is simply outs made by fielders on batters divided by available outs. Actual outs made by fielders (FObat) on batters can be found as:

FObat = (AB - SO - H) + SF + SH

The available outs for fielders (BIP, Balls In Play) on batters can be found, as described above, as:

BIP = PA - SO - BB - HBP - CI - HR

And thus FEbat is just FObat/BIP. That number tends to average about 70% with a by-team range of roughly plus or minus 5%. In 2020, it was 70.41% (0.70413758723829, to be exact), with a range of from 75.24% down to 66.01%.

Note that our definition of BIP is slightly different from the more common one, in that we include sacrifice bunts (SH), because—just like sacrifice flies (SF)—they represent a fielding opportunity to the defense. The percipient will notice that FEbat is very nearly the complement to the now-standard measure BABIP, which tends to run around .300: that is, 1-FObat very nearly equals BABIP. The small difference is that SH factor. We include it because a poor-fielding team will convert some SH attempts into base hits or ROE (“Reached on Error”), while a good-fielding team will have few or no such flubs. Incidentally, we first developed—and published—the FEbat stat (under a slightly different name) about four decades ago.

We said above that there are actually two categories of “possible play”; let’s now look at the second, outs made by the defense on runners who have already reached base safely. Such outs, which we call FOrun, are fewer than FObat, but each such out is a bit more important in that it removes a base runner. Those kinds of outs are often felt to be the cream of defense: double plays (and the occasional triple play), caught stealings, pickoffs, outfield assists, and suchlike.

For FErun, the “available outs” are simply all runners who reached base safely (OB, On-Base). That can be expressed as:

OB = PA - SO - (FEbat x BIP)

That is, it is all batters who came to the plate minus those who made out (which last is strikeouts and batters put out by the fielders).

The “actual outs” on base runners can be reckoned as follows:

FOrun = OB - (R + LOB)

By the rules of scoring, every batter must end up in one of three statistical categories: an Out, a Run, or a Left On Base. So, if we subtract Runs plus Left On Base from the total of men who initially reached base safely, we get the number put out on the bases.

Thus, the second team-fielding measure, FErun, is simply FOrun/OB. That number tends to average about 9% (.09)—for 2020, it was 9.18% (0.091846758349705, to be exact).

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Estimating Team-Fielding Runs

Elsewhere on this site, in the daily stat tabulations, we show individual team fielding and FE numbers. But neither an FE (nor a Jamesian DER) directly answers the question of how fielding affects run scoring, and thus wins. Fortunately, with a little thought we can use the FE to analyze with reasonable accuracy the contributions (always at the team level) of fielding to total defense. We do that on the page linked at the head of this paragraph, and so won’t here repeat the explanation of the mechanics of how it all is done. (But for those interested in the tiresome details—and who have looked at that page first—we have a separate page on the mechanics of calculating the effects of team defense on team stats and defensive results.)

What we will say here is that the data show that fielding is almost certainly not over 20% of total defense. Defense being almost exactly (see the note above) 50% of the game, fielding is thus not over 10% of the total game. Something like 40 years ago, we wrote that fielding was about 5% of the total game; we now know that that was an underestimate, but it wasn’t a grotesque underestimate; pitching still outranks fielding by about a 9:2 ratio (speaking just of the defensive side of the game).

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