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Fantasy Baseball: Busting the September Pitching Myth

Jake Ciely August 24, 2017 9:25AM EDT
Sometimes in sports, theories turn into narratives and then into assumed “facts.” One such case is the assumption that September presents a great opportunity to find pitching due to the numerous call-ups as rosters expand. The assumption is that with lesser-quality batters finding their way into lineups regularly, starting pitchers post better numbers. I went into this last Fantasy Baseball piece for 2017 planning to look at potential upside starters for September with this thought in mind. After pulling the data though, not only was I surprised by the results, I dug back five years to make sure last season wasn’t an outlier and found that the September narrative is a lie!

This week, we’re busting the September pitching myth!

As always, we use SOBB (breakdown here) as the initial base when projecting a pitcher’s future performance.

Range of starting pitcher SOBBs (K-BB%) and the values they hold.

SOBB Rating
20.00-plus Terrific
16.00-19.99 Great
13.00-15.99 Good
11.00-12.99 Average
8.00-10.99 Poor
under-7.99 Awful

Range of relief pitcher SOBBs (K-BB%) and the values they hold.

SOBB Rating
25.00-plus Terrific
20.00-24.99 Great
16.00-19.99 Good
12.00-15.99 Average
8.00-11.99 Poor
under-7.99 Awful

Cheers or Tears for the September Narrative

The first thing I noticed is that the number of starters with a SOBB of 20-plus was much lower than I expected with just 12 starters hitting that mark. Okay, maybe some of last year’s young studs threw these numbers off or it was a one-year blip. Let’s check the 2016 numbers on their own first. It turns out that September was the second lowest month for starters with a 20-plus SOBB. April saw 19, May 11, June 17, July 16 and August 13. Additionally, dropping down to 18-plus SOBBs, which is still great, we had 25, 20, 31, 29, 29 and 20 starters, meaning September tied May for the lowest. Looking at these numbers, it’s clear that there is no advantage for starters in September, and in fact, it’s one of the worst months of the year for strikeout numbers… at least for 2016. Let’s take this further and go back five years.

Taking the 2012-16 seasons for qualified pitchers to get a solid sample, it turns out this wasn’t just an anomaly. In April, there are 19 starters with a SOBB of 20-plus and 25 total of 18-plus. In May, it’s 11 and 20, June is 18 and 31, July is 17 and 29, August is 12 and 28, and September is down near May again at 12 and 20. Those numbers are almost exactly in line with the 2016 numbers on their own. Now, we can see there is a clear trend through the season of starters beginning strong, fading in May, peaking in June and August and again, fading in September. The May swoon makes sense, as that’s often when we hear about starters going through a “dead arm phase.” September is strange, though. You would assume lesser quality batters would help, but it appears the starters wear out and/or lose effectiveness late in the year.

Let’s dig in a bit more, though, and look at ERA in addition to SOBB. Maybe, batters are just making more contact and hitting into outs versus swinging and missing more frequently. Well, bad news September narrative believers. The ERA marks tell us it’s all a lie too. By month, the number of 2016 starters with a high-quality ERA (sub-3.00) goes April 33, May 28, June 29, July 35, August 26 and September 24. Even taking it further to usable starters with a sub-4.00 ERA doesn’t make things better, as the numbers turn to 59, 60, 54, 63, 58 and 45. The biggest argument for September is that it’s easier to find usable starters. September has the lowest number of starters with a high-quality SOBB and usable ERA than any other month.

We’ll do the same practice and look at the last five years just to make sure this isn’t a one-off year either (by now, you can probably guess the results). Starters with a sub-3.00 ERA and total with a sub-4.00 by month are April 33/59, May 28/59, June 29/54, July 34/62, August 26/58 and September 22/42. The ERA marks aren’t even close to the SOBB marks when September was in line with May and the dead arm period. September simply falls behind by a large margin in both ERA ranges. In fact, ERA mimics the SOBB marks for the high and low month, which is rather interesting but not that surprising considering how SOBB predicts success.

Here are the full charts for easier viewing:


SOBB 20+191117161312
SOBB 18+252031292920
Sub-3 ERA332829352624
Sub-4 ERA596054635845


SOBB 20+191118171212
SOBB 18+252031292820
Sub-3 ERA332829342622
Sub-4 ERA595954625842

I don’t know about you, but I am extremely surprised by these numbers. It’s been repeated so many times for so many years that September is the easiest month to find cheap starters because the call-ups water down the quality of batters. It turns out that assumption is not only unfounded, it’s a straight up lie and can ruin your season! Chasing starters in September can and will actually ruin your chances at winning your league, as the data clearly shows. ERAs are up, strikeouts are down and this September narrative is busted. Stick to your quality starters as you chase your league title from now on while valuing starters more in the second half and finding some value trades next May.

Streaming Pitchers to Target Next Week (Last 30 Days Stats)

Mets: 18.3 SOBB, 25.5 K%, 84 wRC+

Brewers: 17.3 SOBB, 26.0 K%, 84 wRC+

Padres: 17.1 SOBB, 24.6 K%, 85 wRC+

White Sox: 16.8 SOBB, 23.6, 92 wRC+

Avoid! (Besides the Astros and Dodgers)

Angels: 7.0 SOBB, 16.3 K%, 109 wRC+

Reds: 7.8 SOBB, 19.6 K%, 106 wRC+

Main Image credit: Carlos Herrera/Icon Sportswire

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