THE BOOK--Playing The Percentages In Baseball

Tuesday, August 09, 2011

Rays v Tigers: Common Opponents

The Detroit Tigers are 61-53.  The Tampa Rays are one game back, at 60-54.

When the NHL expanded from six to twelve teams, the NHL new that to give the expansion team a fighting chance, they’d have to put all six expansion teams in the same division.  By letting the original six and expansion six have limited games against each other, it guaranteed that the expansion division would “look” competitive.  But, in terms of head-to-head, the original six decimated the expansion six.

MLB, while nowhere near to this extent, has this kind of issue with the AL East.  That is, since the Rays play against slightly tougher competition than the Tigers, it makes it harder for the Rays to pile up wins.

One way to show this is to look at “common opponents”, and in the same proportion.  For example, since the Tigers never played the Reds, Marlins, Astros, Brewers, and Cardinals, we throw out all those 21 games from the Rays.  So, gone are the Rays’ 12-9 record from those games.  At the same time, the Tigers never played the DBacks, Rox, Dodgers, Mets, Pirates, and Giants.  So, out goes their 7-11 record.

So, against common opponents, we are now at 54-42 for Tigers and 48-45 for Rays.

However, the Rays faced the Orioles 12 times, while the Tigers faced them only three times.  So, what we do is pro-rate the record of the Rays against the Orioles down to 3 games.  So, instead of being 6-6 against the Orioles, we make them 1.5-1.5.  We repeat this with all the common opponents.

With 75 “matching” games (out of the 114 they played), the Tigers end up with 41 wins, and the Rays end up with 37 wins.

When I started this, I expected the Rays to be ahead of the Tigers, reasoning that the Rays had the tougher opponents.  As it stands, they did have slightly tougher common opponents.  But the two things that conspire against the Rays:
a. among the teams that only one of them played against, the Rays did much better, but all those games get thrown out
b. when the Tigers and Rays went head-to-head, the Tigers won all three games

Now, obviously, we don’t want or need to throw games out.  We would simply do a strength of schedule adjustment with all the teams.  Once you do that though, you are doing an indirect approach.  You are comparing the Rays against NL Central with the other teams (not Tigers) also against the NL Central.  And then you are comparing the Tigers against the NL West with the other teams (not Rays) also against the NL West.  With those common baselines now in place (i.e., rest of league against NL West and NL Central), we presume that we can fairly compare the Rays and Tigers indirectly.

We could do that.  But I’m not doing that here.  In the process I’ve laid out here, we’re doing a direct comparison.  And under the direct comparison, the Tigers are 4 games ahead of the Rays.

(Glove-slap to Max for inspiring this.)

Note: as an example of why it’s unfair to ignore the indirect methodology: the Rays could have been 21-0 against the NL and the Tigers could have been 0-18 against the NL, and under the direct methodology, all those games would get thrown out.