Baseball Reference only has WPA or Win Probability Added going back to 1945. The idea is that every hit, walk or out a player makes either increases or decreases his team's probability of winning. Players who hit well with runners on base or in the late innings of close games will tend to score higher.
Barry Bonds has the three highest WPA totals ever. Our player in question has the 4th best. Bonds had 12.95 in 2004, 11.48 in 2001 and 10.49 in 2002. So in 2004, the Giants won 12.95 more games with Bonds than they would have if an average hitter were in his place.
Here are some clues about the record holder before Barry Bonds:
He is in the Hall of Fame
He was MVP in the year he broke the previous record.
The player whose record he broke is also in the Hall of Fame and was also MVP the year he set the record.
Our player, not surprisingly, led his league in SLG and OBP.
Our player is also among the all-time leaders in WPA.
He batted .349 with runners in scoring position in his record year.
His SLG was .678 with runners on base.
In close & late situations, he batted .390.
In close & late situations, his SLG was .792.
Click here to see who this player is and his splits for this record year
Click here to see the single season leaders
Click here to see the career leaders
Click here to see the progressive leaders