There is no need to beat around the bush with an intro full of cliches and examples. Simply does playing in the postseason wear down a player enough to effect their next season’s production?

Simple answer: Not really.

Less simple answer: Some with hitters, not at all with pitchers.

Complex answer: Danger math.

To answer this question, I just compared four sets of data (2010 to 2018) for both pitchers and hitters. Here are the four datasets (same label at the tables).

Regular: Regular season stats for the season playing in the postseason.

Regular season stats for the season playing in the postseason. Postseason: Postseason stats

Postseason stats Steamer: Steamer projections

Steamer projections Next Season: Stats from the next season.

For hitters, I used OPS since I’m able to convert changes in OPS to changes in roto categories. For pitchers, I used ERA. I found the average and median changes in each player’s stats. I prefer the median value since it helps to remove extreme values that can occur, especially with ERA. I’ll start examining the hitters. Here are average and median differences.

Median Change in OPS for Postseason Hitters Postseason PA Postseason – Regular Steamer – Regular Next Season – Steamer Next Season – Regular > 70 -.078 -.031 -.005 -.034 60 to 69 -.113 -.033 -.015 -.052 50 to 59 -.128 -.023 -.013 -.038 40 to 49 -.131 -.031 -.026 -.041 30 to 39 -.106 -.008 -.014 -.026 20 to 29 -.132 -.007 -.011 -.028 10 to 19 -.162 -.010 -.018 -.032 1 to 9 -.464 -.001 -.023 -.029 Overall -.184 -.011 -.017 -.033

Average Change in OPS for Postseason Hitters Postseason PA Postseason – Regular Steamer – Regular Next Season – Steamer Next Season – Regular > 70 -.078 -.031 -.005 -.034 60 to 69 -.113 -.033 -.015 -.052 50 to 59 -.128 -.023 -.013 -.038 40 to 49 -.131 -.031 -.026 -.041 30 to 39 -.106 -.008 -.014 -.026 20 to 29 -.132 -.007 -.011 -.028 10 to 19 -.162 -.010 -.018 -.032 1 to 9 -.464 -.001 -.023 -.029 Overall -.184 -.011 -.017 -.033

It’s not surprising to see hitters really struggle in the postseason with the improved pitching. Also, the hitters likely over-performed and were due for some negative regression as seen in a lower Steamer projection compared to the previous season.

The “Next Season – Steamer” column is the key data. Hitters underperform the next season by about 15 to 20 points of OPS. This difference works out to about 1 HR over 600 PA and 6 points of AVG. Not a ton but definitely a tiebreaker.

And now to the pitching data

Median Change in ERA for Postseason Pitchers Postseason IP Postseason – Regular Steamer – Regular Next Season – Steamer Next Season – Regular >= 25 -0.20 0.39 -0.06 0.41 20 to 25 0.01 0.66 -0.02 0.43 15 to 20 0.34 0.50 -0.18 0.23 10 to 15 -0.11 0.64 -0.18 0.46 5 to 10 -0.11 0.61 -0.06 0.54 < 5 -0.86 0.58 -0.02 0.60 Overall -0.20 0.57 -0.07 0.51

Average Change in ERA for Postseason Pitchers Postseason IP Postseason – Regular Steamer – Regular Next Season – Steamer Next Season – Regular >= 25 -0.06 0.42 -0.08 0.33 20 to 25 0.00 0.57 -0.01 0.56 15 to 20 0.57 0.48 -0.12 0.36 10 to 15 0.05 0.57 0.03 0.60 5 to 10 0.52 0.58 0.24 0.82 < 5 3.60 0.51 0.37 0.88 Overall 2.08 0.53 0.25 0.78

I didn’t expect several of these outcomes. Yes, the pitcher’s projected ERA was going to regress, but the regular to postseason results stayed almost constant using the median values. Also, the pitchers next season results were just a bit better than the projections. It even holds true for pitchers who throw a lot (> 20 IP) of postseason innings which everyone worries about.

The numbers say anywhere from a 0.05 to 0.10 lower ERA than the projections. I’m not sure what narrative(s) should explain the results. None is probably the correct answer. I’ll go with that the a pitcher who is healthy and good enough to throw a bunch of postseason innings is healthy and good enough to throw a bunch the next season.

The key is that I’m not going to ding the value of Strasburg, Cole, Greinke, Verlander, or Scherzer because of the deep post-season run. But I hope others do. For hitters, I may shy away a bit.