The 1989-90 offseason: in 1989, McGwire batted .231/.339/.467, which represented his worst batting average performance. He only increased his output to .235/.370/.489 the next season.
After he was injured in 1993: if he intended for steroids to help, they may not have worked. He was limited to 172 PAs in 1994 and didn't stay on the field for an extended period of time until 1995 (422 PAs).
"On occasion" throughout the 1990s, including 1998: This period was naturally when McGwire emerged as one of the premier sluggers in all of baseball.
McGwire admitting his steroid use does clear the air and ceases the arguments concerning the validity of his statistics. However, it remains to be seen what kinds of effects the revelation will have on baseball statistics as a whole.
What we do know is that the single-season home run list is now topped with admitted and suspected steroid users:
Barry Bonds - 73
Mark McGwire - 70
Sammy Sosa - 66
Mark McGwire - 65
Sammy Sosa - 63
Sammy Sosa - 62
Roger Maris - 61
Babe Ruth - 60
Babe Ruth - 59
Jimmie Foxx - 58
Hank Greenberg - 58
Ryan Howard - 58
Mark McGwire - 58
I suppose that means that Ryan Howard will soon be accused of using steroids very soon. ;)
When players hit 50 home runs in a season these days, it seems to automatically make them steroid user suspects in people's minds. This can't go on forever, though. At some point, fans must realize that there are factors in most eras in baseball history that skew statistics. It just so happens that this is one of those eras that involve performance enhancers.
AP Photo by V. J. Lovero