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Team Defense, 2018


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Evaluating Team Defensive Performance

Through games of Sunday, 30 September 2018.
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.


2018 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  
TOR1626265557814753253220855112986718483135394301.72683200
TOR1626183550514563213220554412816618473133384301.739797-4-4
KAN162628456031543271362055491157512357160324296.72683000
KAN162620355311523267362025421142502356159324296.739796-4-4
CIN162627956051491291272285321258504348182234323.72882900
CIN162621055431475288272255261244494347181234323.739799-4-4
BAL162634056251552325342345891203671742086424293.72889600
BAL162626655601534321342315821189661742085424293.739864-4-4
NYY162614155431311293131774941634581729088314369.72466500
NYY162606054691294289131754871612571729087314369.740635-4-4
MIN162628755601425280261985731377802549084284330.72878400
MIN162621754981409277261965671362792548083284330.740756-3-3
SDG162625455911430283321855191399683639188304371.72874900
SDG162618855321415280321835141384673639187304371.739723-3-3
PIT161614455061380287261744971336693735070354302.72971300
PIT161608454531367284261724921323683735069354302.739690-3-3
PHI162613854901366292321715001465603945499354337.72970200
PHI162608254401354289321694951452593945498354337.739680-3-3
TEX162623155971516325442224911121722050174184293.73483700
TEX162619455641507323442214881114722050174184293.739822-2-2
STL162627155061354242261445931337675550046134366.73368800
STL162623554751346241261435901329675550046134366.739675-2-2
CLE162607155661349311232004071544591621281284372.73367200
CLE162603655341341309231994051535591621281284372.739659-2-2
BOS16261665515130624735176512155884946063304376.73567100
BOS16261405492130024635175510155184946063304376.739661-1-1
NYM1626178554113642412418548414467142400130364382.73570300
NYM1626156552113592402418448214417142400130364382.739694-1-1
CHW1626339553114052932419665312598918471133394311.73781800
CHW1626324551814022922419665112568918471133394311.740813-1-1
DET162613055051423278342164911215601657178364276.73877000
DET162612254981421278342164901213601657178364276.739767-0-0
LAD162606155331275242251774181559602423370244401.73961300
LAD162606055321275242251774181559602423370244401.74061300
SEA162607355451396289231954001328721242266264346.74068400
SEA162607855501397289231954001329721242266264346.73968600
COL162611954681369265481825231399522547491254333.74171200
COL162612854761371265481825241401522547491254333.739716+1+1
SFO162619155251387291421565241269454948093314384.74269800
SFO162620755391391292421565251272454948093314384.740704+1+1
ARI162613954951313259191745221448572934265274389.74765200
ARI162618255331322261191755261458572934265274389.740667+2+2
HOU162591353651164257211524351687661234160254365.75053800
HOU162596354101174259211534391701671234161254365.740555+2+2
WSH162608754531320273261984871417762941175434338.74768600
WSH162613154921330275261994911427772941176434338.740703+2+2
MIA161623654721388309231926051249713848260424326.74775600
MIA161628355141399311231936101258723848260424326.739774+2+2
LAA162610854451353256192055461386651435346334312.75070500
LAA162616554961366258192075511399661435346334312.740727+3+3
ATL1626155539312362482615363514235239351101284370.75764700
ATL1626255548012562522615564514465340361103284370.739682+4+4
MIL162608353871256239401725501420614241268394356.75764800
MIL162618054731276243411755591443624342269404356.739684+5+5
TAM162599253821236262201645011421531639176264345.75960000
TAM162609854771258267201675101446541640177264345.740639+5+5
CHC162622854661307220281576221327663735282394402.75966900
CHC162633955641330224281606331351673836283404402.739709+5+5
OAK162609955171303268191844741237532330296464397.76264700
OAK162622956351331274191884841263542331298474397.739696+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 14% 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 Monday, 1 October 2018, at 6:32 am Pacific Time.