The Value of Defense

Defensive Sabermetrics
As Sabermetrics progress, stats become more accurate and cover more ground. Recently some of the best out there have been turning their attention to defense.

Usually when people talk about defense, they like to phrase it in the following format:
Player X is (an all-star, above average, an asset, terrible) because his defense is worth (exactly the amount of runs it would take to prove the point in question), didn’t you see (one random play in a sample of hundreds that is indisputable evidence of player x’s greatness/deficiency). It’s an exercise in selective memory and egregious misuse of numbers

Recently, a few people have begun to think that defense is the next OBP. As it becomes more and more quantifiable people say that it is the most undervalued stat around. Defense is a skill that contributes to a team’s success. Not quantifying it into an evaluation of a player is foolish if there is a way to quantify it. Luckily, there is.

But how much is defense worth????
As the Mariners found out, on a team basis this is very valuable, on an individual basis, it is still worth a good amount. The Bill James Fielding Bible lists all players on a plus/minus scale. The info is compiled by Baseball Info Solutions. They describe the methodology on the site, but it appears that each play is painstakingly reviewed, and all plays a player makes that at least 1 player missed is worth +1, all plays a player misses that at least one player made is worth -1. While objective, this has been hailed as the best system ever, as a masterpiece, I’d say it really adresses the problem with things like zone rating and would say this is one of the best systems available now. The +/- system does what many people would say is ideal the way to evaluate defense, but wouldn’t even dream of investing the time to actually compile. Overall, a play is valued as slightly less than half of a run (no explicit formula stated). So what does it say???

At every position there are a few guys worth at least a win over the average defender. Albert Pujols (+37 plays) is worth about 17 runs, or 1.7 wins just with is glove. Derek Jeter (-34) is at -15 runs. (I use +/-*.45 and round). For a majority of players the results are pretty small.

Mariners players in the top 10 or bottom 5 at their positions
Player +/- approx. runs
Richie Sexson -15 -7
Adrian Beltre +7 +3
Raul Ibanez -23 -10
Ichiro! +4 2

All players are not listed (only the top 10 and bottom 5), but it is pretty safe to assume that all other players are worth between -2 and +2 runs, and at that level I wouldn’t feel confident saying a player was below or above average. Next time you compare Ibanez to the average player, subtract 10 runs, his defense cost the team a win. His Base Runs Above Average rated him at 32 runs; you can factor his defense down to 22 runs above average. Still a good player, but that difference is quite a few OPS points.

Can it be used?
Defense matters. There is likely to be improvements as with all stats, but the numbers at the fielding bible site are pretty good numbers to apply to players, and I would have no problem using them. It should be noted that the baseline is a .500 defender, while replacement level is I believe in the .350 range, so combination with VORP is not applicable, only metrics against the average player. I think defense can be used as an advantage in roster construction, like OBP was. OBP wasn’t used to figure out that Albert Pujols was a good player; it was used to discover Scott Hattebergs. It is possible that some team could garner an advantage this way. Suppose you have two guys, one is +10 runs with his bat and average with his glove, the other is average with his bat and +10 with his glove. Both players would rate as equal in your system, but the first player is going to be more expensive, and even if he was rated slightly higher, the salary difference would likely make the second player a much more money-efficient choice. As defensive metrics improve and more and more teams jump on the bandwagon, it is likely that teams will in fact add accurate defensive numbers like these to their ratings. As with OBP, the first teams to do so will a) run the risk of this whole thing being bologna and blowing up in their face and b) run the risk that they will have more accurate rating systems and will find many players at salaries that are much lower than their values and reap the advantages while other teams catch up.

Conclusions
1. I am willing to say that BIS’ ultra-thorough method of looking at every single play is good enough for me to consider this a good start, and I am willing to say you can put a run value to defense and that this is a pretty close approximation.
2. As with all statistics, more data is good, using 3-year aggregate data is going to be a better way to evaluate a defender, unless you have reason to believe (injury, age decline) that he is not the same defender.
3. If defense is quantifiable, and I believe it is, than teams that incorporate defense into their player evaluation methods, whether on data from BIS or their own, stand to take a competitive advantage over the teams that do not.

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3 Responses to The Value of Defense

  1. marc w. says:

    What do you make of the lack of agreement between the PBP metrics derived from BIS data compared with metrics derived from STATS data?

    Take a look at Ichiro, or Grady Sizemore…. both UZR, say, and THT’s RZR would agree that these guys are exceptional. One thinks they’re exceptionally good and the other exceptionally bad.

  2. ksks2 says:

    Good questions. In response to the specific case you cited, Ichiro! is actually ranked 10th in RZR and also 10th in +/-, sizemore is 12th in RZR and in neither the top 10 or bottom 5 in =/-. Ichiro is in the average/slightly above for both, and Sizemore is behind him for both, neither thinks either player is exceptionally good or bad. It should also be noted that these are different systems, +/- takes into account speed of the ball, defensive shifts, etc that rzr doesn’t. so they don’t necessarily have to match up, that they do shows that defensive stats are improving. John Dewan is actually the guy who created both. Zone rating was so flawed he came up with RZR, and then decided that it would be even more accurate to go with +/-.

    As to the difference, that is a problem that comes up not only on defence but also in pitching and hitting. I’m not going to pretend i have an answer to that. it is a problem that hopefully gets fixed, some things (flyballs, popups, “fliners”, liners) are natural to get confused, but i believe there were even discrepancies on fb/gb data. to say one source is better than the other is wrong, we just don’t know who is more accurate yet.

  3. ksks2 says:

    In looking at it again I feel I did state it too strongly. i don’t think this stat is beyond improvement. right off the top of my head i can say i think it needs to be normalized to chances by position. (who is better, ichiro with +10 plays in 200 chances or ibanez with +8 in 160 chances (#’s made up). right now the stat is kind of like vorp. vorp doesn’t care if you had 900 pa’s, or if you hit .560 on BIP, it is what it is and +40 in 750 pa’s is rated higher than +39 in 350 pa’s. I don’t think defensive stats are perfect. i feel the methods of +/- are the best available, and that on top of that they are pretty darn good.

    i don’t know if defense will ever be able to be graded as accurate as offense. i do think you can get pretty accurate though, and a big part of my point was that teams that ignore it are going to be left behind, and that teams that use defense extensively stand to gain an advantage. specifically, using multi-year data will likely generate an improvement and prediction methods for future defense will improve as well.

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