Similarity Scores

Similarity scores compare the statistics of baseball players with one another to determine how closely related player’s performances are. The formula can be found at Baseball-reference. Basically, the comparison between two players starts at the number 1000, and points are subtracted for discrepancies with the two player’s statistics. For example, for batters one point is subtracted for each difference of 20 games played, for each difference of 75 at bats, for each difference of 10 runs scored, and so on. For pitchers, one point is subtracted from 1000 for difference of 1 win, for each difference of .02 in ERA, and so on. The full formula is at the link mentioned above. The closer the number is to 1000, the more similar the statistics are.

Its fun to check out a player’s similarity scores to see how closely related their stats are with other players. The player page on Baseball-reference shows full career comparisons as well as age comparisons. The age based similarity scores compare an active player’s career to another player’s career up to that specific age. This is where you can make some very interesting comparisons like Delmon Young, through his age 21 season, was most similar to Hall of Famer Tris Speaker through his age 21 season. Miguel Cabrera is very similar to Hall of Famer Frank Robinson through his age 28 season, but he was most similar to Hank Aaron and Ken Griffey, Jr. earlier in his career. Eight of the ten players Cabrera is most similar to through the age 28 season are in the Hall of Fame or will be in the Hall of Fame. I think Miggie might join them if he keeps producing the way he is.

Some career similarity scores are almost predictable. Chuck Knoblauch and Eric Young were both undersized middle infielders who eventually shifted to left field. They both have a career batting average in the .280’s and Knoblauch had only 200 more at bats. It seems like the only difference between the two players is amount of hatred Minnesota fans have for them.

2011 NL Cy Young Award Winner Clayton Kershaw is most closely related to Vida Blue and Dontrelle Willis through their age 23 seasons. Each of those players had Cy Young type seasons at a very young age; Blue won the MVP and Cy Young at age 21 in 1971 and Willis was Rookie of the Year at age 21 and runner-up for the Cy Young at age 23 in 2005. Vida Blue was good; I don’t think the Dodgers would mind if Kershaw had a career like him.

As a Royals fan, I see a lot of frustration with Billy Butler and his lack of any discernable skills besides hitting. I don’t buy it. He has a good on base percentage, but people think his bulky size should mean he hits for power. Comparable players through age 25 are John Olerud, Kent Hrbek, and Keith Hernandez. That’s pretty much spot on except for Hernandez’s defensive prowess. All of these players weren’t flashy, but they just hit the ball.

We’ll let you know other interesting comparisons if we come across any. Let us know some good ones you find as well.