"They may top his records. You always get topped, you know. But in his day he had no equal."
-- Chief Meyers in "The Glory of Their Times," about Jim Thorpe
There is an aura of timelessness about baseball's most hallowed records, which belies the impact of the era and conditions in which they were set. And no records in baseball are more sacrosanct than those for home runs.
The most notorious example of the circumstance-specific nature of home run records, and baseball's obsession with them, was commissioner Ford Frick's July 1961 decree directed at Roger Maris' ultimately successful chase of Babe Ruth's single-season record of 60 home runs. Frick ruled that, because the regular-season schedule that year had been increased from 154 to 162 games (to accommodate expansion in the American League), any season record set after 154th game would be branded with a Scarlet "A" (an asterisk).
Similarly, some would emblazon the career home run record about to be seized from Henry Aaron by Barry Bonds with an "S." No Frick-like pronouncement, however, has been forthcoming, nor is one expected.
We at Imagine Sports make no judgments regarding such matters. We do not simulate player performance based on moral judgments or subjective suspicions of the impact of alleged steroid use by particular players. What we can do, however, is replay Aaron's career as if it had been contemporaneous with that of Bonds.
Whether it was primarily steroid use, or some combination of factors, that noticeably boosted home run output throughout baseball since 1993, the end result can be "injected" (so to speak) into Aaron's career (1954-76), by replaying it contemporaneously with the "Bonds era" (1986-2007) using the rates of offense for those years. Aaron played one more season than Bonds has played to this point (Aaron spent 23 years in the bigs), so we simulated Aaron's career as if the overall rates of offense prevailing from 1954-76 were those of 1984-2006.
We replayed each season of Aaron's career 20 times, as if it had taken place in the hitting environment of the corresponding season 30 years later, and averaged the results. Aaron finished his simulated career total of 766 home runs, 11 more than his actual total of 755, and just enough to leave in doubt whether Bonds would be able to catch and pass him -- at least before the end of the 2007 season.
Here are the results of our simulations, compared to the actual career records for Aaron and Bonds:
Perhaps the most significant feature of these results is that, halfway into his "sim" career, Aaron was 50 home runs behind his actual career pace. The reason is that the 1950s, when Aaron began his career, actually were more offensively-oriented than the 1980s, when Bonds began playing. Aaron begins making up the home run difference when his seasons from the 1960s, at which time pitching was more dominant, are shifted to the homer-happy 1990s. He finally passes his actual career total when his twilight 1970s seasons are shifted to the new millennium.
More offense also means more at-bats, and Aaron, who achieved his actual HR total over nearly 1,500 plate appearances more than Bonds has had in his career, racked up an additional 387 plate appearances in his sim career. Other factors that may have favored Aaron (or Bonds) from season to season include the parks they played in and the protection they received in their teams' lineups (Bonds has received a career record 676 intentional walks compared to 293 for Aaron).
Aaron's best real-life single-season HR total was 47 in 1971, which was replayed as 2001 in our simulations. It so happens that 2001 also was the season when Bonds broke the single-season record with 73 homers. Although Aaron averaged "only" 55 home runs in 20 simulated 2001 seasons (eight more than his actual 1971 total), he achieved some impressive individual season results: He hit 61 homers or better in five (out of 20) of his 1971/2001 seasons, topping out at 67 in Season 10. He also hit 61 and 64 in 1967/1997 Season 11 and 13, 61 in 1969/1999 Season 8, and 60 in 1973/2003 Season 5.
Although we draw no inferences regarding the steroid controversy from our comparison of their careers, it does appear that the career patterns of Henry Aaron and Barry Bonds are really not as dissimilar as many claim. As critics frequently have noted, Bonds did indeed increase his HR output later in his career, but the first half of his career was played during a period that was tougher for hitters than beginning stages of Aaron's.
Nevertheless, Aaron's best single-season homer output (47 in 1971) occurred at age 37, which corresponds to Bonds hitting 73 in 2001 at age 36. In fact, there is little difference between Aaron's simulated seasons and the corresponding actual seasons for Bonds -- except for that magical 2001 season. It also should be noted that Bonds, even with the loss of most of the 2005 season to injury, has managed to sustain his HR output a little longer than Aaron did.