Stat scape

How long can Barry Bonds, 41, strike fear in the hearts of National League pitchers? The problem for forecasters is that no previous slugger has been so productive at such an advanced age.

Yes, he may have been steroids-aided, but set that issue aside for now. Based strictly on the numbers, Bonds is in a class by himself. None of the 10 sluggers deemed most similar to Bonds by Baseball-Reference.com can match his late-career production. Jimmie Foxx was done at 34, Lou Gehrig at 35, Mickey Mantle and Mel Ott at 36. Frank Robinson and Babe Ruth reached their finish lines at 40, as Rafael Palmeiro probably will. Ted Williams hit well in part-time duty at 41, but Willie Mays and Hank Aaron were shells of their former selves in their final seasons at 42.

Bonds, by contrast, has gotten more powerful with age. The chart compares his performance in slugging to that of two stellar groups: the sluggers most similar to him and all 56 outfielders in the Hall of Fame. So that players from different eras can be compared fairly, we focus on slugging average (total bases divided by at-bats, denoted SLG) relative to the league in a given year (denoted SLG+). If one player slugged .600 during a homer-happy season in which the league SLG was .400 and another slugged .500 in a league with an average SLG of .333, both are assigned an SLG+ of 150, signifying both were 50 percent above the league average.

Through age 26, Bonds tracked nicely with the performance of the Hall of Fame outfielders. From age 27 through 34, he took it to the next level, slugging on par with the elite 10. Then, he surpassed even them.

Of course, that unprecedented surge often is cited as possible evidence of steroids' effects. But maybe it's not as suspicious as it seems. Slugging ability declines slowly--but unevenly--as players age. The 10 hitters most similar to Bonds outslugged their leagues by 57 percent at age 25 but still exceeded league norms by 45 percent at 37. The Hall of Fame outfielders' SLG+ was 133 at age 27 and still 122 at 34.

Although late-career power surges are unusual, they're not unprecedented. Seven of the Hall of Fame outfielders had power spikes in their mid- to late 30s that exceeded their earlier peaks. Ted Williams outslugged the league by 79 percent at 24 and 80 percent at 38. Hank Aaron had an "off-year" at 36, posting an SLG+ of 137, but came back strong the next year with a career-high SLG+ of 172.

Bonds' late surge simply is more dramatic and persistent than Aaron's--or anyone's. We'll never sort out how much, if any, of his power is owed to chemicals or medical technology Mantle never had or training methods Ruth never had. The only certainty is that we've never seen anything like this.

Steve Walters

E-mail him at swalters@loyola.edu.

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