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Team Defense, 2019


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Evaluating Team Defensive Performance

Through games of Monday, 30 September 2019.
All results are from true, unadjusted data.

(You can also read a fuller discussion of this Table.)


Team Defense Evaluation

(Please see the page of this site that deals with fielding for background summaries.)

What we want to see is the effect of fielding on runs allowed and thus games won. The easiest way to do this is to see how the team is actually doing, then see how it would be doing with an all-MLB-average level of fielding. There is no 100% exact way of doing that, but we can make a pretty good approximation.

We make a few assumptions to begin with. First, we assume that the number of outs made is invariant—that is, the team would have played the same number of defensive innings with average fielding as it actually did. While theoretically better or worse fielding could change the number of extra-inning games, or games with no bottom-9 half, the assumption is by and large a good one, so we make it (because without it, we can't really get anywhere).

Next, we assume that the rates of things that pitchers control would remain the same no matter the fielding. Those things include the so-called "three true outcomes" (walks, strikeouts, home runs) plus hit batsmen. Those also are perfectly reasonable assumptions.

We will further assume that the rates (per plate appearance) of sacrifice bunts and sacrifice flies are invariant with changes in fielding. That is less likely to be exactly so, but the total numbers of sacrifices are quite small compared to the big-ticket out-making items like strikeouts and ordinary fielding putouts, so any difference that better or worse fielding might introduce would be trivial.

We know, of course, that the number of plate appearances depends on the on-base percentage: the higher the OBP, the more men will, on average, get to come to the plate before the third out of the average inning. The converse of OBP is the outs rate: if the team has an opposing-batters OBP of .333, then the team has an outs rate of .667. Changes in fielding obviously change the outs rate, and thus the total plate appearances (here more rightly called "BFP", Batters Facing Pitchers) of the opponents. If we can reckon the change in the defensive outs rate, we can calculate the change in the BFP and thus in all the team defensive stats.

The outs rate has two components: strikeouts and fielders' outs. Fielders' outs are simply all non-strikeout outs, which is innings pitched times three minus strikeouts. Note that the fielders' outs rate is not simply the number of batters put out by the fielders: it also includes an especially important aspect of fielding, outs made on runners who have already safely reached base (a class that includes double and triple plays, caught stealings, pickoffs, and outs on runners trying to advance).

The strikeout rate is simply K/BFP taken from the actual team stats. To get a useful FO (Fielders' Outs) rate, we need to relate actual FO not to PA but to BIP (Balls In Play). As we said above, the BIP rate (BIP/PA) we assume to be invariant; its components are At-Bats, Strikeouts, Home Runs, and Sacrifices. The equation is just:

BIP = AB - K - HR + SF + SH

What we here call FE ("Fielding Efficiency") is just FO/BIP. We can readily calculate the all-MLB average FE, and use that to do our projecting.

What we do is, for each team, calculate its actual FE and its actual BIP rate, using actual data. We then apply that all-MLB FE to the BIP rate (which rate, remember, we are reasonably assuming to be invariant); that gives us the projected FO rate if the team had a perfectly average defense.

Finally, we add that projected FO rate to the known (and invariant) Strikeout rate to get a projected total Outs rate; from that, using the invariant total Outs number, we get the new, projected BFP total for the team, if it had average defense.

We can now take the ratio of those BFPs to the actual BFPs and use that ratio to pro-rate all the actual stats into projected average-defense stats. (Naturally, we round all those pro-ratings off to whole integers.)

Now we have two team-defense stat lines: the actual one, and the one they would have with perfectly average defense. For each, we then calculate, using the established runs- produced equation, the normally expected runs for each, which allows us to see how many runs the team's fielding has saved or cost it so far this season.

(We use calculated runs even for the actual-data line, rather than actual runs, because we want to compare apples with apples: the actual team runs allowed will almost always differ somewhat (usually but not always a small somewhat) from the calculated value from sheer luck, and we are interested in the effects of fielding, not the outcomes of luck.)

To look at the impact of those runs lost or saved, we use a quick-and-dirty approximation, simply dividing the runs difference by the average number of runs per game in the appropriate league (which is typically the number of runs needed to change the win total by one game). That isn't exact, but it gives a reasonable engineering approximation.

You can see the results of all this, right up to date, in the Table below.


2019 Team Defense, Tabulated

Listed in ascending order (worst first) of fielding quality based on Fielding Efficiency.

For each team, the first line is actual data and the second projected stats with all-MLB average defense. FE is "Fielding Efficiency". The ΔW is the current difference in team wins attributable to fielding; ΔWyr is that difference pro-rated to a full season.

— Team Stats — — Calculations —
Team G BFP AB H 2B 3B HR BB SO HB SH SF CI SB CS Outs FE OR ΔW ΔWyr  
DET161634156641555315442505361368692546197374299.71291500
DET161620455421521308432455241338682445195364299.735854-7-7
PIT162639156481511351342415841443853436471294320.71389900
PIT162626455351481344332365721414833335470284320.735843-7-7
SDG162616055511394302222154631475684335058184296.71675500
SDG162605654571370297222114551450674234057184296.735713-5-5
TEX162635456291515310322415831379701950381264314.72088300
TEX162626455491493306322385751359691949380264314.735844-5-5
MIN162624656711456282231984521463612040271164390.71974000
MIN162615655891435278231954451442602039270164390.735704-4-4
BOS162639956601423319262156051633761838270314413.71980200
BOS162630955801403315262125961610751837269314413.735766-4-4
COL162642356921576325442705891264574243075304346.72694700
COL162636956451563322442685841253574243074304346.735923-3-3
KAN162630755761525299282215821230811849157274275.72685900
KAN162625455291512296282195771220801849157274275.735836-3-3
NYM1626232560114052871920450015206035351139224383.72575000
NYM1626178555313932851920249615075935351138224383.735729-3-3
WSH162613454911340281182025171511612737186244318.73171600
WSH162611054701335280182015151505612737186244318.735706-1-1
SEA162626856521484336242605051239511246283264318.73185300
SEA162624556311479335242595031234511246283264318.735844-1-1
BAL162639656971544311313055611248801046282254329.73495600
BAL162638756891542311313055601246801046282254329.735952-0-0
TOR162631355901450340232286041332691136374364321.73383400
TOR162630255801447339232286031330691136374364321.735830-0-0
CHC162619054921377265251955341444802949691254326.73373800
CHC162618054831375265251955331442802949691254326.735735-0-0
ATL162624355571421253232035481393693927376204352.73575700
ATL162624255561421253232035481393693927376204352.73575700
NYY16261335535137427718248507153444736471244329.73675100
NYY16261405541137627718248508153644736471244329.73575400
CHW161615954661438278192385821312512038276264238.73681500
CHW161616754731440278192385831314512038276264238.73581800
LAA162628955751417284282675761404821243199354328.73985100
LAA162631055931422285282685781409821243199354328.735860+1+1
MIL162625155421364247362255701497604334294344378.73976700
MIL162627555631369248362265721503604334294344378.735777+1+1
CLE162600854491308315202074501508621730053284313.74266900
CLE162604454821316317202084531517621730053284313.735683+2+2
TAM162608655311274264261814531621601128375354423.74462100
TAM162613155721283266261824561633601128376354423.735637+2+2
PHI162627455711452249232585461392714640066504361.74181800
PHI162630956021460250232595491400714640066504361.735833+2+2
ARI162623055681400289292205161427623939647314395.74274500
ARI162627156051409291292215191436623939647314395.735761+2+2
SFO162625655971395244372275191368654133188334407.74676100
SFO162631856521409246372295241382664133189334407.735786+3+3
CIN162605753951270260192145361552583631188264314.74768800
CIN162612254531284263192165421569593631189264314.735713+3+3
LAD162591353871201239241853921519663036263174337.75258100
LAD162600054661219242241883981541673037264174337.735614+4+4
HOU162599554611205233212304481671411130475174387.75462300
HOU162609155491224237212344551698421130476174387.735660+4+4
OAK162615355411342249232014771299662542283414395.75468600
OAK162626256391366253232054851322672543284424395.735728+5+5
MIA162624754731340281272366151378902939157244333.75278200
MIA162634855611362286272406251400912940158244333.735823+5+5
STL162606853891284246191915451399692738034194332.75965400
STL162620155071312251191955571430712839035194332.735704+6+6
Team G BFP AB H 2B 3B HR BB SO HB SH SF CI SB CS Outs FE OR ΔW ΔWyr  

Conclusions About Fielding Significance

From the data tabulated above, we can draw conclusions about the relative significances of fielding and of pitching to total defense.

We first reckon the average difference in runs that fielding alone contributes; for each team, we take that difference and divide it by games played, to get a "fielding-runs per game" number, which we then divide by 30 to get a team-average fielding effect. Next, we reckon the all-MLB average runs allowed and reckon, for each team, the difference between that and the fielding-neutralized runs allowed by that team (and again divide by games played); that gives us the difference from average for that team attributable solely to actual pitching, because fielding has already been neutralized to average. When we divided that sum by 30, we have the average difference in runs that pitching alone contributes. If we then sum those two figures—fielding effects and pitching effects—we get the total average difference from team to team on defense. We can then see what fraction of that total came from fielding alone and what fraction from pitching alone.

The results so far this season are these:

And, total defense being 50% of the game, fielding is thus 13% of the total game of baseball. Is that figure perfectly exact? No. But it's probably within a couple of percent either way. Certainly it is quite indicative of relative significance.




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This page was last modified on Tuesday, 1 October 2019, at 6:33 am Pacific Time.