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Team Defense, 2017


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Evaluating Team Defensive Performance

Through games of Wednesday, 28 June 2017.
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.


2017 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  
NYM773093273673713310111292681281720040142086.70942400
NYM773007266071712910108284662271719039142086.739388-5-9
SFO81317728637911502991239631242922045212191.71241500
SFO81309227867701462889233614232821044202191.740380-4-9
BOS7829202682684140129319972317418036212087.72233300
BOS7828762642674138129219671217418035212087.739316-2-4
PIT78301927337321711489219576282710245162105.72637700
PIT78298126987231691488216569282710244162105.739362-2-4
BAL773070270876713610116299557291024038192063.72844000
BAL773035267875813410115296551291024038192063.739425-2-4
OAK78297726536851311595247618341029466222055.72637900
OAK78294026206761291594244610341029465222055.739364-2-4
DET7729522633715133159926458325821140222024.72839000
DET7729192604707132159826157725821140222024.739377-2-3
TOR77293926456611471095244687241015152122067.73135100
TOR77291726256561461094242682241015152122067.739342-1-2
PHI772992266072914110111258572272126028132061.73639800
PHI772982265172614110111257570272126028132061.739394-1-1
NYY7628692588609109792231717231214132112043.73531200
NYY7628572578607109792230714231214132112043.739308-0-1
TAM8030662740687153989262649261721044112151.73635700
TAM8030572732685153989261647261721044112151.739354-0-1
ARI79297226686251251578249730152019138152130.73731000
ARI79296726636241251578249729152019138152130.739309-0-0
KAN76290125986741191184248585241219038182035.74034000
KAN76290325996741191184248585241219038182035.73934100
MIN762986265270212311112267535351418037152045.74139700
MIN762992265770312311112268536351418037152045.7393990+1
WSH78295026566571231099228705321617145142101.74133800
WSH78295426596581231099228706321617145142101.7393400+1
MIA76293625626371371781299603362514037172024.74135500
MIA76294225676381371781300604362514037172024.7393570+1
STL77296526436591241689245653322124029142097.74233800
STL77297326506611241689246655322124029142097.7393410+1
HOU7929622669617134139423980530910552112136.74431900
HOU7929742680619135139424080830910552112136.7393230+1
CLE772811255261413349021975921712028222039.74329500
CLE772821256161613349022076221712028222039.7392990+1
ATL77298926606891469102258549292616051142075.74437900
ATL77300326736921479102259552292616051142075.739384+1+1
SDG78295426266701329102260643401414040142065.74536200
SDG78297026406741339103261646401414040142065.739369+1+2
COL81309827447031342296281646302022133142172.74737300
COL81312027637081352297283650302022133142172.740382+1+2
MIL80309127467081591899282633321813052142161.74738500
MIL803114276771316018100284638321813052142161.739395+1+3
CHC78294426296311271297262686251314163172091.75034000
CHC78297326556371281298265693251314164172091.739351+1+3
LAD80292526505981101184218756211917033212149.75528100
LAD80296426856061111185221766211917033212149.740295+2+4
TEX7829832660695128410426655027822042162083.75336700
TEX7830242696704130410527055727822043162083.739383+2+4
CHW7728972570640131121022795892461624372022.75435700
CHW7729372606649133121032835972461624472022.739373+2+4
CIN77300826236951509129302596382321138222057.75242000
CIN77304626567041529131306603382321138222057.740437+2+4
SEA80303927237071306125255578231422242122130.75538800
SEA80308627657181326127259587231422243122130.739408+2+5
LAA82304627496761249114243691251314235262193.76234500
LAA82311028076901279116248705261314236272193.739370+3+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 Thursday, 29 June 2017, at 6:32 am Pacific Time.