The Cardinals’ Impressive Winning Streak Doesn’t Guarantee October Success

With a doubleheader win on Friday, a bizarre 3-2-5-4-2-8-6 double play and a ninth-inning comeback on Saturday, and more late-inning heroics on Sunday, the Cardinals ran their winning streak to a franchise-record 16 games. The streak is the longest in the majors since Cleveland won 22 consecutive games in 2017, and the longest in the National League since the Giants won 16 in a row in 1951 as part of the comeback that culminated in Bobby Thomson’s pennant-winning homer, “The Shot Heard ‘Round the World.”

The Redbirds’ winning streak has turned a team that was 71-69 with just 5.0% Playoff Odds into one that’s on the verge of cinching the NL’s second Wild Card spot, suddenly giving the Cardinals a look of invincibility. “With 16 Straight Wins, the St. Louis Cardinals May Never Lose Again,” reads one headline. “Cardinals Look Unstoppable Right Now,” reads another.

For as unbeatable as the Cardinals appear right now, the history of late-season winning streaks tells us that while this run may certainly help the team secure a playoff berth, it doesn’t tell us anything about how they’ll fare in October. Look no further than that aforementioned Cleveland team for a harsh reminder of that lesson. From August 24 to September 15 of the 2017 season, the defending AL champions steamrolled opponents, piling up wins in close games and in blowouts until they’d set an American League record. The team finished with 102 wins, the highest total by the franchise since 1954, and hopes were high that they could secure the title that they’d come so close to winning just the year before. Yet when the postseason rolled around, Cleveland was unceremoniously bounced, losing a tight five-game series to the Yankees.

The story was similar for the team whose AL record they broke. The 2002 A’s won 20 straight games from August 13 to September 6 and finished with 103 wins, the franchise’s highest total since 1988. Yet they too were defeated in a five-game Division Series, losing to the Twins.

In fact, no team that’s run off a late-season streak — starting in August or September — of more than 11 wins has even reached the World Series during the division play era (1969 onward):

Prior to this season, nine of the 12 teams with late streaks of 12 wins or more made the playoffs, seven of them by winning the division. That tally stands to improve given that both the Cardinals and Yankees currently occupy Wild Card spots, though the latter hardly has things sewn up. This year’s teams aside, of the group above only the 2017 Diamondbacks, who won their Wild Card game before losing to the Dodgers in the Division Series, and the 2004 Astros, who beat the Braves in the Division Series before falling to the Cardinals in the NLCS, even advanced in the playoffs. That none of these teams, even those with 100-plus wins, played further into October is quite a fluke, but it just serves to remind that these winning streaks don’t guarantee anything.

Interestingly enough, several teams with late-season winning streaks that ended right at 11 games fared better than those with 12 or more wins:

Here 11 of the 15 teams with late-season streaks of exactly 11 wins made the playoffs. Seven of them won at least one postseason series, and five won the pennant, but only the 1970 Orioles, the middle child from a run of three consecutive pennant winners, brought home the World Series trophy; they did so by beating the Reds in a five-game series. There’s no particular reason why these teams with shorter winning streaks than the first group would have more postseason success, but that’s the way it’s crumbled, cookie-wise.

Considering those two groups together touches upon a point I’ve made annually for over a decade, based on studies that I did while writing for Baseball Prospectus and then SI.com: there’s no correlation between a team’s performance in September and its subsequent performance in October. I first wrote about this in 2009, examining 112 playoff-bound teams from 1995 to 2008 and how each performed in their final seven, 14 and 21 regular season games as well as those from August 31 to the end of the season, which sometimes trickles into the first week of October (for the rest of this piece, I’ll refer to this as September records or September winning percentage despite the spillover). At each of those increments, what I found was an essentially random relationship between the winning percentages in those fragments and the results of the Division Series — correlations ranging from -0.042 to 0.019, a whole lot of nothing.

That was a very counterintuitive finding, given that just two years earlier, the 2007 Rockies had won 13 of its final 14 games, including a Game 163 tiebreaker, and stormed through the postseason field before being swept by the Red Sox in the World Series. That run made it easy to forget counterexamples such as the 2006 Cardinals dropping nine of their final 12 regular season games yet winning the World Series, or the 2000 Yankees going 3-15 over their final 18 games, evoking comparisons to the 1899 Cleveland Spiders given the lopsided run differential during that stretch yet winning their third straight championship.

I reprised that study in 2017, dispensing with the “week” intervals but adding 2009-16 data to the mix, and again found no predictive relationship between September record and October success. That piece goes into circulation around this time every year, but with my address having changed from SI.com to FanGraphs, I figured it was worth revisiting again, this time by including 2017-19 data as well; alas, last year’s pandemic-shortened 60-game season and the novel playoff structure with the extra round meant that I couldn’t include the data.

So here we are, this time covering the September and October performances of 216 teams from 1996-2019. These teams combined for a regular season winning percentage of .582, and as a group improved down the stretch, winning at a .578 clip through August, and a .600 clip in September, an uptick that serves as an opportunity to note the selection bias at work. While 27 teams did back into the playoffs with records below .500 after August 31, many clubs who entered September in playoff positions did badly enough that they didn’t make the cut at all, and so their October results can’t be tracked. For example, this year’s Padres entered September at 72-62, half a game ahead of the Cardinals for the second Wild Card spot, but they’ve since gone 6-16 and been eliminated; they and their ilk thus don’t have October showings to compare to their September bellyflop. Oddly enough, the lowest September winning percentage of any Wild Card-era playoff team was the 1998 Padres’ .375 (9-15) — yet they reached the World Series before being swept by the Yankees.

So, here’s what I’ve found:

I’ll begin the guided tour by noting that I’ve broken out a separate set of correlations covering only teams in the two Wild Card era, lest the evidence point to conditions that have changed dramatically from the single Wild Card era (it does not). The first row compares the correlations between a team’s full regular season winning percentage over 162 games (give or take one due to tiebreakers and rainouts) and its postseason winning percentage. As you can see, there’s a faint relationship visible, the strongest of any in this particular set but not very strong at all.

The second line is the correlation between regular season winning percentage and postseason win total, because really all that matters is getting to 11 wins by winning the Division Series, League Championship Series and World Series, or 12 wins if the team has gone the Wild Card route. It doesn’t particularly matter how many times a team loses so long as it doesn’t hit three or four at the wrong time; a division winner that goes 11-2 in the postseason team and one that goes 11-8 will both be champions. The third line shows the correlation between regular season winning percentage and the number of postseason series won. Here I should note that these correlations are slightly higher than those from the 2017 study, which came in at 0.24 for postseason winning percentage, 0.17 for postseason win total, and 0.15 for postseason series win total.

Those correlations are pretty slight, but still considerably more robust than what comes next, as the September winning percentages just don’t tell us very much at all about what happens in October. Again, these figures are a bit ahead of the numbers in the 2017 study (0.09 for postseason winning percentage, 0.03 for postseason wins, and -0.01 for postseason series wins) but that’s not saying much at all. For each category, the full season winning percentage is much more predictive than the September winning percentage.

Within this study there are a few other interesting findings to update:

I noted above that the postseason teams collectively did improve in September, which makes sense, but what’s at least somewhat interesting is that the World Series winners (and losers) did not; their level of play as judged by wins and losses was unchanged, possibly because the typical late-season gains by some teams were offset by others that had the breathing room to rest their fatigued or injured players late in the year.

As previously noted, a total of 27 teams have made the postseason despite sub-.500 September records; the White Sox (11-12 this month) could run that count to 28, and even the Yankees (13-12) could wind up in that group if the other remaining AL teams fail to capitalize. Only four teams have won the World Series after a sub-.500 September — the aforementioned 2000 Yankees (13-18) and 2006 Cardinals (12-17), plus the 1997 Marlins (12-15) and 2015 Royals (15-17) — but five others have won pennants, most recently the 2017 Dodgers (13-17). The September Stumblers, who won at just a .446 clip down the stretch after playing .598 ball prior, nonetheless compiled a .527 winning percentage in the postseason, which is to say that they fared better than the average postseason team, since the group collectively produced a .500 record.

With one more win or losses by both the Phillies and Reds, the Cardinals (20-6 this month) will clinch that second Wild Card spot, and their epic winning streak will be part of the story. They may or may not have another October run in them, but don’t fall into the trap of believing that this winning streak is the reason why.