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.