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Team Defense, 2019


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Evaluating Team Defensive Performance

Through games of Thursday, 22 August 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  
PIT127498244071168275261854541121632729256273378.71569000
PIT127489343281147270261824461101622728255273378.735653-5-6
DET126493143971186251331904211040502042176313360.71869400
DET126485743311168247331874151024492041175313360.734661-4-5
COL128503344921234253382024391018373035055233423.72172300
COL128496744331218250371994331005373035054233423.734692-4-5
SDG126478543321093237151673441124523324048153349.71858300
SDG126471442681077233151653391107513324047153349.734554-4-5
TEX129506644921211252281884581101571640375173444.71970300
TEX129499344271194248281854511085561639374173444.734672-4-5
BOS129505744941130256231724561282631428250233496.71863300
BOS129498644311114252231704501264621428249233496.734605-3-4
WSH127484943481087221161563981169542028169213385.72258100
WSH127479342981074218161543931156532028168213385.734559-3-4
SEA1284944447912022581721738097536939164183395.72669300
SEA1284902444111922561721537796736939163183395.734674-2-3
NYM1274886437311032281715940611624927301103173422.72759500
NYM1274853434310962261715840311544927301102173422.734582-2-2
MIN127490344461128212161593641105481628153143450.72757600
MIN127486944151120211161583611097481628153143450.734563-2-2
ATL129503144531160199201654651110553521265143464.72863600
ATL129500044261153198201644621103553521265143464.734624-2-2
KAN12849654389119323122170454981681539042223379.72866300
KAN12849364364118623022169451975681539042223379.734651-1-2
BAL1285056449812312552426045698356737259203394.73179000
BAL1285038448212272542425945498056737259203394.734781-1-1
MIL127495743791113198311834621154503430270273430.73364000
MIL127495043721111198311834611152503430270273430.735637-0-0
LAA13050394486114222722208450114661734186313470.73267700
LAA13050304478114022722208449114461734186313470.734674-0-0
TOR13050444473116426517184483105551925356313460.73666400
TOR13050514479116626517184484105651925356313460.73466600
NYY12948984429112122614210398117531531457173440.73562300
NYY12949024433112222614210398117631531457173440.73462500
CHW127485143081140231181854511011431730257233334.73564600
CHW127485543121141231181854511012431730257233334.73464800
ARI128491243921122233241674001106473731533233461.73958800
ARI128493344101127234241684021111473731533233461.735597+1+1
CLE128474542981025249141623521189551624041233410.74452300
CLE128478343331033251141633551199551624041233410.734537+2+2
CIN126472142091013200121694231216422422166193348.74354700
CIN126475542401020201121704261225422422166193348.734560+2+2
CHC127480142801064219121623941108582538663163390.74356100
CHC127483743121072221121633971116582538663163390.734575+2+2
PHI126488743481137199192044221068553428052383396.74264300
PHI126492143781145200192054251075553428052383396.734657+2+2
SFO128493844231118193251854041090542828174283471.74361100
SFO128497844591127195251864071099542828175283471.734627+2+3
TAM129483243931004208201413631291411023255313526.74648200
TAM129488244381014210201423671304411023256313526.735500+2+3
LAD12946994295968190211462991182502429245153449.75146300
LAD12947674357982193211483031199512429246153449.735487+3+4
HOU12947704341963191161893571305331026362143479.75450700
HOU12948494413979194161923631327341026363143479.734537+4+4
OAK12848844381106720221152392988502337173333469.75255100
OAK128496544541085205211553991004512338174343469.735583+4+5
STL126470441701013197131524231075552630024183343.75652100
STL126479842531033201131554311096562731024183343.734556+4+6
MIA126480642161020211181874751085661731146203355.75959200
MIA126491243091043216181914861109671732147203355.734635+5+7
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 13.5% 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 Friday, 23 August 2019, at 6:32 am Pacific Time.