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Team Defense, 2018


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Evaluating Team Defensive Performance

Through games of Sunday, 24 June 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  
BAL76301626897561691810027460230617048212040.71542600
BAL7629382619736165189726758629617047202040.742392-4-9
TEX79307027607441691810622857045102703882108.72541100
TEX79301727137311661810422456044102703782108.742388-3-6
COL78302026757111412797278669281424137112084.72739300
COL78297626367011392796274659281424136112084.743375-2-5
PIT77294426496591411483235641261717036162065.72734000
PIT77290126116491391482232632261717035162065.742324-2-4
KAN773031270174413819111266550271323124132064.72941700
KAN772991266673413619110263543271323124132064.742400-2-4
TOR772980266168716179726464829520160212063.72937700
TOR772943262867815979626164029520159212063.742362-2-4
NYM75290125856601141099246690301921057172031.73035600
NYM75287025576531131098243683301921056172031.742343-2-4
LAD76290626256221211378226721261315139102074.73030900
LAD76287325966151201377223713261315139102074.742297-2-3
PHI75280625126181221074221684281922444191997.73130500
PHI75277924876121211073219677281922444191997.742295-1-3
SDG80304827226831241987261681281918039162142.73435400
SDG80302427006781231986259676281918039162142.742344-1-3
MIN74287625536331281091250665391420036112013.73633900
MIN74286025396291271090249661391420036112013.742332-1-2
CIN773008265670013417109284589211730033142069.73839600
CIN772996264569713317109283587211730033142069.742391-1-1
CHW772996260566515298632056440724057192031.73938300
CHW772985259566315198631956240724057192031.743379-0-1
STL7629562594621102157126864739272802642074.73931800
STL7629472586619102157126764539272802642074.742315-0-1
BOS7929762677614123187124376532420030112143.73929700
BOS7929672669612123187124276332420030112143.742294-0-1
SFO79300526786771451667261604232419044162121.74033300
SFO79299826726751451667260603232419044162121.742331-0-1
SEA7829302664663143138920467539616136162099.74132600
SEA7829262660662143138920467439616136162099.743325-0-0
CLE762852262561814710961857022866236112070.74430600
CLE762856262861914710961857032866236112070.74330700
MIA78302626586781561097296619282122124252094.74337200
MIA78302826606781561097296619282122124252094.74237300
NYY752812252655511687823476629716033132040.74727400
NYY752823253655711687823576929716033132040.7422780+1
DET78297126456731321797257587341024143142077.74736300
DET78298426566761331797258590341024143142077.742368+1+1
LAA78297726606501271210027171428313216132110.75033800
LAA78299626776541281210127371928313216132110.743346+1+2
OAK782970269666212810100221583281014152222114.75234200
OAK782996272066812910101223588281014152222114.743352+1+2
HOU792859260553812677320782730413036122142.76424300
HOU792909265054712877421184131413037122142.743259+2+4
WSH7628022533578140148721171533817037262050.76028700
WSH7628452572587142148821472634817038262050.743303+2+4
TAM77285825605861319792426352582213482063.76129000
TAM77290826045961339802466462582213582063.743308+2+4
ARI7728782582600128487233666271420225142086.76229200
ARI7729302628611130489237678271420225142086.743311+2+5
ATL76290125515891261575292680252012138122075.76330400
ATL76295525986001281576297693252012139122075.743323+2+5
MIL77286325185641001980275676282119233162063.77029300
MIL77293325795781021982282692292219234162063.743318+3+7
CHC7528822503557971372326639241811035162048.77429400
CHC75296525755731001374335657251911036162048.742323+4+8
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 14.5% 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 Monday, 25 June 2018, at 6:32 am Pacific Time.