Bill Mazeroski's Fielding-An Essay on Fielding Statistics

By Clifford Blau

Several weeks ago, Mike Emeigh posted an article to rec.sport.baseball and to his Web site (http://www.geocities.com/Colosseum/Stadium/8957/index.htm). In it, he analyzed the value of Bill Mazeroski's fielding. He calculated the value of the extra putouts, assists, and double plays made by Maz. He found that Mazeroski saved the Pirates an average of 57 runs compared to the other National League second basemen during the years 1957-68. (Mr. Emeigh subsequently expanded the study by two years and produced a figure of 51 runs per annum. His most recent revision resulted in a finding of 25 runs per 162 games. I believe Mr. Emeigh has dealt as well as possible with the question given the available data. After my original article, I have summarized some comments and data provided by other SABR members on this question.)

I realized that 57 runs is a lot of runs, and that if it were true that Mazeroski's fielding were that valuable, it would be possible to corroborate the fact in other ways. The typical difference between an average defensive team and the best is about 100 runs, so if one player were accounting for over half that much with his fielding, it should stand out. I will state here that I found no certain answers. While I think it unlikely that anyone's fielding could be so valuable, I will here present what evidence I have. I will make use of comments made during a discussion of Mr. Emeigh's article on the SABR e-mailing list as well as other research. Any other facts that anyone can contribute to this study are welcome.

The Big Picture

Mr. Emeigh, in making a case for Mazeroski's Hall of Fame candidacy, stated that Maz' value was equal to that of an average fielding second baseman who created 57 runs above average each year. I decided to test this by looking at the performance of teams who had such players. I looked for players who created 57 runs above average (for the league, not position.) There were very few players who did that for as many as a dozen years. I identified 14 such players. Leaving Ruth and Gehrig out, since they were teammates for much of their careers, I looked at a dozen great hitters. They collectively created an average of 55 runs above average over their best 12 consecutive seasons. Their teams had a collective winning average of .565. 57 runs over a 162 game season should produce approximately 6 extra wins, or a winning average of .537 for an otherwise average team. The Pirates during the years 1957-1968, when Mazeroski was their regular, full-time second baseman, had an overall winning average of .517. More to the point, the teams with the great hitters scored a park-adjusted 50 runs above average, very close to what was produced by their leading hitters. The Pirates during 1957-68 allowed just 21 runs below the league average, park adjusted. On this basis, it seems unlikely that Mazeroski was saving 57 runs a year. It should be noted that Rogers Hornsby's teams during his prime had only a .499 winning average, and that Stan Musial's Cardinals scored only 25 runs above average while he was creating 60. Thus, it is not outside the realm of what we may construe as normal variation that the other Pirates may have been far enough below average defensively over those dozen years to neutralize some of the effect of Mazeroski's fielding.

Further, if Mazeroski's fielding were so valuable, then pitchers being traded to the Pirates would tend to have a lower ERA than they'd had the previous year. Likewise, pitchers traded by the Pirates would see theirs rise. In fact, a group of 7 starting pitchers traded to the Bucs during those years saw their adjusted ERAs rise by .07, while the one starter traded away by them improved his adjusted ERA by .17. On the other hand, in 1969, when Maz missed most of the season due to injury, the Pirates adjusted ERA went from 107 to 97.

A second claim that Mr. Emeigh made is that Mazeroski took away an average of 46 hits per season compared to his peers. If this were so, the Pirates, all other factors being equal, would have had an opponents' batting average .008 below average. Their actual batting average allowed was .004 above average. Part of this .012 difference could be due to Forbes Field. It was a slight hitters' park, although it was very tough to hit home runs in. To what extent it increased batting average, I do not know, but obviously it did. (My subsequent research covering the years 1957-1962 shows that opposing players' batting averages were .002 higher at Forbes than in Pirates' road games.)

Methodological Flaw

Mr. Emeigh gave Mazeroski credit for all plays he made above average, without consideration of factors other than Maz' skill that may have influenced the statistics. He converted the extra outs to runs using Pete Palmer's Linear Weights formula. To see the error of this, take an extreme example. Imagine a pitcher throws a perfect game, consisting of 27 routine ground outs to second. If the league average number of chances per game for a second baseman were 5, the second baseman would get credit for taking 22 hits away from the opposition and making 22 additional outs, yielding a runs saved value of 16. The pitcher, assuming a league ERA of 4.00, would get credit for 4 pitching runs. The other 8 fielders would presumably be charged with allowing 16 runs above average, although they had no chance to save or allow runs. The point is that while opportunities to make plays will not be as absurdly distributed as in this example, they do not even out. All chances above average do not represent plays that an average player would not have made in the same circumstance. Many factors affect how many chances a second baseman has besides his skill, and we cannot make proper allowance for all of them.

Significant Factors

The Pirates' pitching staff during the years 1957-68 struck out .45 batters below average per 9 innings. This obviously meant more chances for the infield and outfield. Indeed, the Bucs' shortstops over that period averaged .4 chances per game more than their peers, their third basemen had an average number of chances, and their outfielders collectively had .3 extra chances per game. It is not clear from this distribution whether the Pirates' pitchers tended to allow an above average number of ground balls. Under the assumption that ground ball pitchers allow fewer home runs than average, I determined that on a park-adjusted basis, the Pirates allowed .6% more homers than their peers. Thus, while it appears that some of Mazeroski's extra chances were due to there being more batted balls than normal against his team, we cannot say to what extent he benefited from that.

Stats Inc. tracks the location of all batted balls. Using their statistics for 1989, 1990, and 1992, I found that the number of balls hit into the second baseman's zone varied by as much as 204 between 2 teams in the same league in a season. The standard deviation for a season was 48, and over the three years, one team had 224 balls below average hit in the second base zone. Defensive average, which uses different, larger zones, shows larger differences. Thus, Maz' additional 90 chances per season could be entirely due to extra balls being hit near him, rather than to his skill.

Minor or Unknown Factors

Charles Pavitt concluded in his study of the effect of pitchers on fielding statistics that teams with an above average number of innings thrown by right handers will have an above average number of chances by their second basemen. Since the Pirates averaged only 1% more innings by righties than the rest of the league, this is not a significant factor in evaluating Maz' fielding statistics. Likewise, teams that allow a lot of baserunners will make more double plays on average. The Pirates during the years 1957-68 had an opponents' on base average .001 above the league average, while surrendering .135 home runs fewer per 9 innings, and their games were .01 innings longer than the mean. This boils down to about 20 extra baserunners per year, which could account for about 1.5 of the extra double plays in which Mazeroski participated. Michael Mavrogiannis and John Henry Rickert, using a different methodology, reached about the same conclusion. Thus, the number of baserunners is not a significant factor in the number of double plays made by Maz. However, this does not mean that the remaining 29.5 DPs were due to his skill, since we do not know how many double play opportunities he had.

Paul Schwarzenbart, in the initial issue of The Baseball Analyst, showed that ballparks have as much, if not more, influence on fielding statistics as they do on hitting and pitching numbers. Since we do not know what the fielding park factors for Forbes Field were, we cannot tell whether this helped or hurt Maz' stats.

Summary

Mr. Emeigh assumed that Mazeroski was solely responsible for all extra chances and double plays credited to him, and that an average second baseman would not have made those plays. Actually, many factors influence fielding statistics, and one should not assume that a player's defensive value is accurately portrayed by them. Other facts, such as the Pirates record and number of runs allowed during Mazeroski's career suggest, though do not prove, that his defensive value was much less than the 57 runs calculated by Mr. Emeigh.
 

Updated Commentary


Several people contributed ideas and data to the discussion of this issue on the SABR mailing list, in particular John Rickert, Tom Ruane, and Rich Hansen, as well as Mike Emeigh. I will herewith attempt to summarize the key points.

The ratio of a team's infielders' assists to its outfielders' putouts acts as a good surrogate for the groundball to fly ball ratio of a teams' pitching staff. While both of these ratios are affected by the quality of the fielders as well as the pitchers' groundball/flyball tendencies, they do help to estimate the extra chances Maz may have gotten as a result of the type of pitchers used by the Pirates. Also, as noted above, the Pirates had more balls in play against them than the average team and had used right handed pitchers slightly more than the average staff. These three factors were estimated by Mr. Emeigh to increase Mazeroski's chances by 7%.

Other Pirates, filling in for Mazeroski while he was injured, made nearly as many double plays per game as he did (.804 versus .815), indicating that a large portion of the extra double plays may have been due to circumstance rather than skill.

A large portion of secondbasemen's putouts, about 55-60% on average, come on balls which they do not field, mainly forceouts. A smaller portion of their assists, about 15%, similarly come on balls others fielded. Mr. Emeigh calculated that, due to the groundball tendencies of the Pirates' pitchers, all, and then some, of Mazeroski's additional putouts were a result of simply catching throws and were not reflective of fielding value. Tom Ruane found, using a small sample, that about 35% of a second baseman's chances are on balls they don't field.

Rich Hansen, using Retrosheet files for the 1967 and 1982 American League seasons, published data on double plays. He found for 1967 that actual double play opportunities, meaning groundballs with a runner on first and fewer than two out (accounting for about 70% of double plays,) varied among secondbasemen by as much as .54 per nine innings. In 1982, team double play opportunities for secondbasemen ranged from 190 to 132.

Conclusion

The Mazeroski case presents an interesting example of how difficult interpreting fielding statistics can be. Separating fielding from pitching is perhaps the most difficult task in baseball analysis. While Mr. Emeigh dealt as well as possible with the available information, he was forced to use average where actual information was unavailable. As Messrs. Ruane and Hansen found, actually opportunities can vary widely in a season, or even over several seasons. One should be hesitant to base any decision solely on even well adjusted fielding statistics. It is best to keep this in mind when considering hitting and pitching statistics, too.

Any questions or comments, please e-mail me at CliffordBlau@yahoo.com

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