Only four men have ever hit more than 60 home runs in a single season. In the seven seasons in which they achieved the feat, they racked up 462 home runs between them, or an average of 66 per year.
But not every massive home run season is created equal. Today's graph of the day compares those seven seasons using Rally's batting runs above average (BRAA) from his WAR calculations, Win Probability Added, and Win Probability Added divided by the average Leverage Index, which Tango suggests might be the best way to measure a player's contextual value.
Bonds had by far the most offensive value in his 73 home run season, with Sosa's 2001 and McGwire's 1998 vying for second.
Sosa's 1999 wasn't that impressive a season except for the 63 home runs. It doesn't even make the top 500 seasons since 1954 in terms of WPA. This is just one illustration of why some people question whether he deserves to make the Hall of Fame (ignoring steroids, of course).
For those who are curious, I converted batting runs to batting wins using the simple 10 runs to 1 win conversion. It's not exact, but it's easy and close enough.
The Win Expectancy and Leverage Index data is licensed from http://www.InsideTheBook.com
Batting runs above average from Sean Smith's BaseballProjection site.