Saturday, April 18, 2009

An Early Look at Bill James's Pythagorean Theorem of Baseball

So, the Marlins, at 9-1 have the best record in baseball. This is the same team that Baseball Prospectus (BP) predicted would only win 72 games all year! To reach 72 wins, the Marlins only need to go 63-89 (.414) the rest of the way! Detractors would point out that almost half of the Marlins' wins came againt the lowly Nationals.

And, speaking of the Nationals, BP predicted that the Nationals would go 76-86. To hit that total, the Nationals will need to play .500 ball the rest of the way. Possible? Sure, just about anything is possible in baseball.

But, the bigger question is, how legit are the early returns from the Marlins, Nationals, and other teams?

Let's take a look at Bill James's Pythagorean theorem of baseball, which he created to relate a team's runs scored and runs allowed to its won-lost record. The formula looks like this:

So, based on this theorem, which teams are least deserving of their records? The biggest frauds right now are the Orioles, which have a .600 winning percentage, but only a .396 winning percentage based on the theorem.

The Five Biggest Frauds:

TeamCurrent Winning PercentageExpected Winning PercentageDifference
Baltimore.600.396+.204
San Diego.727.572+.155
Florida.900.752+.148
Cincinnati.556.427+.129
Minnesota.417.297+.120

But which teams are probably better than their record? The most obvious is the Washington Nationals, which have a .111 winning percentage, but project to .357 according to the theorem.

The Top Five Turnaround Candidates:

TeamCurrent Winning PercentageExpected Winning PercentageDifference
Washington.111.357-.246
Colorado.444.592-.148
Tampa Bay.455.585-.130
Pittsburgh.500.607-.107
Texas.400.500-.100

The biggest surprise in this list is the Pittsburgh Pirates, who are 5-5 ten games into the season, but, based on the theorem, project to a .607 winning percentage. To put that numer into perspective, the St. Louis Cardinals won the NL Central last year with a .602 winning percentage.

Colorado might be another team to watch as they project to a .592 winning percentage (The Dodgers won the NL West last year with a .519 winning percentage).

As for the Nats, they're a better team than their record would indicate. That's the good news. The bad news? Their projected winning percentage (.357) is still a pretty poor. But maybe it gives some hopes to Nats fans, who have to be feeling a little better about how their team is playing after a 8-2 shellacking of the Phillies and a heart-breaking 3-2 loss in 10 innings to the Marlins last night. During the first series of the year agains the Marlins (three games in Florida), the Marlins outscored the Nationals 26-13. That's an average of 8.67 runs per game for the Marlins! So certainly holding them to only three runs in 10 innings is a step in the right direction.

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