Another Look at Momentum in October

It’s coming to that time of the year when baseball fans hunker down into their deep-seeded trenches of pro-momentum and anti-momentum factions in regards to playoff baseball. Dave Cameron wrote, just the other day, about how teams that do better in the second half don’t do any better come playoff time, and just about every Baseball Prospectus article these days will mention that narratives can be written either way after the fact, but before the fact, we simply don’t know whether the hot team will “stay hot,” or the struggling team will manage “to right the ship” come playoff time.

Since this post is showing up on FanGraphs, the readers will likely surmise (correctly) that I have historically sided with the anti-momentum crowd. However, an interesting thing happened the other day.

I was trying to make my case to a friend about how hot teams don’t have an inherent advantage, so I made my way over to Baseball-Reference to check in on some of the most recent World Series winners. I wanted to see how they had performed in September (or those few regular season games that spill into October in certain years) to prove that you didn’t need to be hot to end the season in order to capture baseball’s biggest prize. So I started with last season.

As it turns out, the Red Sox went 16-9 over baseball’s final month, which was their second best month of the season. Well, that doesn’t prove anything, it’s simply one year. Then I went to 2012. As it turns out, the Giants went 20-10 from the beginning of September, their best stretch month of baseball all season. Still, that’s only two. The Cardinals of 2011 would certainly be different. Nope. Eighteen and eight, in what was their best month of baseball of the season. This could go on for a while, but let’s simply go to the chart:

 

World Series Champions’ Late Season Success 2002-2013

WS Champ Year Sept/Oct W-L Month W/L% Season W-L Season W/L% Month Rank
Red Sox 2013 16-9 0.640 97-65 0.599 2nd
Giants 2012 20-10 0.667 94-68 0.580 1st
Cardinals 2011 18-8 0.692 90-72 0.556 1st
Giants 2010 19-10 0.655 92-70 0.568 2nd
Yankees 2009 20-11 0.645 103-59 0.636 3rd
Phillies 2008 17-8 0.680 92-70 0.568 1st
Red Sox 2007 16-11 0.593 96-66 0.593 3rd
Cardinals 2006 12-17 0.414 83-78 0.516 5th
White Sox 2005 19-12 0.613 99-63 0.611 4th
Red Sox 2004 21-11 0.656 98-64 0.605 3rd
Marlins 2003 18-8 0.692 91-71 0.562 2nd
Angels 2002 18-9 0.667 99-63 0.611 2nd
214-124 0.633 1134-809 0.584

 

As the reader can see, the World Series champs of the past twelve years were almost always playing some of their best baseball in the final month (with an occasional October nubbin) of the season. Sure, the 2006 Cardinals were under .500, but they were a pretty fluky team in general, owning the fewest regular season wins ever of a championship team. Other than those Cardinals, however, every other team was above .500 during those final four-to-five weeks. And sure, some of that can be explained by the fact that these are top teams who are likely to be nearly .500 or above every month, but in seven of the last twelve years, these teams had either their best, or second best, month right at the end of the season. Their September/October winning percentage was nearly fifty points higher than their season totals, and would be even higher with those strong September/October records removed.

I began to wonder if I had stumbled onto something.

Sure, Cameron and the Prospectus gang had proven that in the Large N analysis of the entire second half and playoffs as a whole momentum didn’t matter, but what about on a smaller scale, maybe this phenomenon did hold some water. So I expanded my search back to the beginning of the Wild Card era, which seemed a natural breaking point given that before 1995 (well, technically 1994, but we all know how that played out) only four teams made the playoffs (which was an expansion from the two teams that made it throughout baseball history until 1969). Let’s check out the chart:

 

World Series Champions’ Late Season Success 1995-2013

WS Champ Year Sept/Oct W-L Month W/L% Season W-L Season W/L% Month Rank
Red Sox 2013 16-9 0.640 97-65 0.599 2nd
Giants 2012 20-10 0.667 94-68 0.580 1st
Cardinals 2011 18-8 0.692 90-72 0.556 1st
Giants 2010 19-10 0.655 92-70 0.568 2nd
Yankees 2009 20-11 0.645 103-59 0.636 3rd
Phillies 2008 17-8 0.680 92-70 0.568 1st
Red Sox 2007 16-11 0.593 96-66 0.593 3rd
Cardinals 2006 12-17 0.414 83-78 0.516 5th
White Sox 2005 19-12 0.613 99-63 0.611 4th
Red Sox 2004 21-11 0.656 98-64 0.605 3rd
Marlins 2003 18-8 0.692 91-71 0.562 2nd
Angels 2002 18-9 0.667 99-63 0.611 2nd
Diamondbacks 2001 14-13 0.519 92-70 0.568 5th
Yankees 2000 13-18 0.419 87-74 0.540 5th
Yankees 1999 17-14 0.548 98-64 0.605 5th
Yankees 1998 16-11 0.593 114-48 0.704 6th
Marlins 1997 12-15 0.444 92-70 0.568 6th
Yankees 1996 16-11 0.593 92-70 0.568 t-3rd
Braves 1995 16-12 0.571 90-54 0.625 4th
318-218 0.593 1799-1259 0.588

 

And wouldn’t you know it. Yet more proof that a big enough sample size can debunk almost any baseball myth. From 1995-2001, there were a pair of losing records, and the best any team did was have their tied-for-third best month of the season. With the addition of only those seven years, the winning percentage that had had such a big gap before is now nearly exactly even in September/October compared to the season as a whole. Now if the World Series rolls around in a month, and the Orioles and Cardinals (the two best September records in 2014, so far) are playing maybe we can pay a little bit of attention to this trend since it has been prevalent for over a decade. But if we get to the World Series and it ends up as a 1989 Bay Bridge Series rematch, with the ice cold A’s, and the only slightly better of late Giants squaring off, we’ll know that once again the large sample size guys have won.



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Mac
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Mac

Ah, good ole regression to the mean