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Team Defense, 2018


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Evaluating Team Defensive Performance

Through games of Monday, 20 August 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  
MIN124484842951113214201504301083662136069213337.72360700
MIN124477042251095211201484231065652135068213337.741576-4-5
PIT126483143261103233211284001009532824051283359.72556700
PIT12647614264108723021126394994522824050283359.740540-3-4
BAL12549084352120625927170454929561234067343325.72668500
BAL12548414292118925527168448916551234066343325.740657-3-4
TOR125482843161143270221634181026471233294323329.72663600
TOR125476342581128266221614121012461233293323329.740609-3-4
KAN12548684315119721728167447899451842142243306.72766300
KAN12548064260118221428165441888441841141243306.740637-3-4
SDG127490443701131221251434141074583031161253411.72759400
SDG127484443171117218251414091061573031160253411.740570-3-4
TEX12749124435121326434177363883581739056153389.73066300
TEX12748634391120126134175359874571739055153389.740642-2-3
NYM1244772427910911861915237910715232300103273349.73157600
NYM1244729424110811841915137610615232300102273349.740559-2-3
CIN12548784339115222521176423951383839159183357.73264200
CIN12548374302114222321175419943383839158183357.740625-2-3
PHI124470242151032212191223681116483136482283351.73451100
PHI124467641921026211191213661110483136482283351.740501-1-2
NYY1244680420697221591403881246501422069233349.73649700
NYY1244664419296921491403871242501422069233349.740492-1-1
CHW124485542321070235161495109556212381104283298.73762600
CHW124484142201067234161495099526212381104283298.740621-1-1
SEA12647584347109923521151315103856929257233398.73854300
SEA12647504339109723521151314103656929257233398.740540-0-0
BOS1264761428698818624129384121552633040203418.73948600
BOS1264756428198718624129384121452633040203418.740484-0-0
LAD12647544322999195201373461199471720256173435.74048800
LAD12647514320998195201373461198471720256173435.740487-0-0
SFO12648384323109922929118408991333638073283425.74054400
SFO12648384323109922929118408991333638073283425.74054400
CLE124461642421025229181522991146461017261223346.74050100
CLE124461742431025229181522991146461017261223346.74050100
STL12648414261102517322109441102258423903893402.74151100
STL12648454265102617322109441102358423903893402.74051300
COL124471341841055203371414241052422039465193313.74156000
COL124471841881056203371414241053422039465193313.74056200
DET12547244248109421526162377925451340163283310.74258300
DET12547324255109621526162378927451340163283310.74058600
MIA12649014303110324719151474984543137244363397.74659900
MIA12649264325110924819152476989543137244363397.740609+1+2
WSH125467142061025218201473561089552033157393345.74651800
WSH125469742291031219201483581095552033157393345.740528+1+2
HOU12545564148901204161193221316491126052203373.74841400
HOU12545854174907205161203241324491126052203373.741425+1+2
LAA12647534238104920319163424108953927234263364.75355000
LAA12648074286106120519165429110154927234263364.741571+2+3
ARI12547064226996200121353851103422130243223391.75348400
ARI125476042741007202121373891116422130243223391.741504+3+3
ATL12447284165976198211264701101393023170183359.75550800
ATL12447914220989201211284761116403023171183359.741532+3+4
TAM12546444159948209141233991078411331151163356.75946300
TAM12547224229964213141254061096421332152163356.740491+3+4
OAK12547384298102621714142357960412021175373411.75750700
OAK12548154368104322114144363976422021176383411.740536+3+4
MIL12747694204981184321454481095483532252263396.75952400
MIL12748514276998187331474561114493633253263396.740555+4+5
CHC12347594152993164201275001006493126161263349.76252100
CHC123485542351013167201305101026503227162273349.740557+5+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, 21 August 2018, at 6:32 am Pacific Time.