Park factors describe how parks affect baseball outcomes on average. But what happens at the extremes? Originally presented at Saberseminar in 2015.

1. Where Park Factors Fail
CASE STUDY OF AN EXTREME PARK EFFECT

2. How do parks really affect outcomes?
Park factors are great!
◦ Calculated as averages, and should be applied to averages
◦ E.g. when calculating wRC+ you adjust baseline up or down based on home park, not the player
But what happens at the extremes?
◦ Do parks really affect all players equally? Probably not.
Difficult to analyze
◦ Measuring a park effect requires large samples
◦ Most parks are fairly neutral
◦ Extreme parks tend to get altered
SABERSEMINAR 2015 @BLABABOUTBALL

3. If only there were an old park with an extreme effect…
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4. (Mostly) unchanged since 1940
At least one extreme park effect
◦ 30%+ impact on doubles, >25% for both LHH and RHH
Fenway fits the bill on both fronts
SABERSEMINAR 2015 @BLABABOUTBALL

5. Found a park… how do we examine it?
Split hitters into extreme groups and see if they’re affected differently
To do that:
◦ Calculate 2B/PA deltas for visitors to Fenway vs. other road games, 1956-2014
◦ Group hitters into quartiles each year by projected 2B/PA rate (using Marcel)
◦ Find weighted averages by quartile and hand
And the results say…
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6. For RHH, Fenway doesn’t discriminate
∆=0.008 ∆=0.004
∆=0.009
∆=0.008
0
0.01
0.02
0.03
0.04
0.05
0.06
1st Quartile 2nd Quartile 3rd Quartile 4th Quartile
Actual RHH 2B/PA rates, by projected rate quartiles
Ex-Fenway 2B/PA rate Fenway 2B/PA delta
SABERSEMINAR 2015 @BLABABOUTBALL

7. What about for LHH?
∆=0.007
∆=0.008
∆=0.009
∆=0.015
1.19x 1.20x 1.21x
1.34x
0
0.01
0.02
0.03
0.04
0.05
0.06
1st Quartile 2nd Quartile 3rd Quartile 4th Quartile
Actual LHH 2B/PA rates, by projected rate quartiles
Ex-Fenway 2B/PA rate Fenway 2B/PA delta
SABERSEMINAR 2015 @BLABABOUTBALL

8. Do Fenway’s changes matter? Yes…
90
100
110
120
130
140
150
160
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Average 2B/PA Fenway Park Effect, by Batter Hand
L (5 yr avg) R (5 yr avg)
SABERSEMINAR 2015 @BLABABOUTBALL
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9. … But not for RHH/LHH weirdness
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Q4 Delta - Q1 Delta, by Batter Hand
L (10 yr avg) R (10 yr avg)
SABERSEMINAR 2015 @BLABABOUTBALL
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10. So what is the explanation?
It’s all about asymmetry:
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Data source: Gameday 2007 hit data, converted to feet using method from Peter Jensen: http://www.hardballtimes.com/using-gameday-to-build-a-fielding-metric-part-1/
75th percentile
distance, by
batter quartile
25th percentile
distance, by
batter quartile

11. Conclusions
Shocking revelation! Some lefties can exploit Fenway’s dimensions more than others.
More interesting: at the extremes, park effects can impact different types of players differently
But… there may not be another park effect like this one, now or ever
SABERSEMINAR 2015 @BLABABOUTBALL

12. Questions?
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13. Appendix: Pitchers are not the difference
Avg 2B/PA allowed vs. batter hand Avg wOBA allowed vs. batter hand
Batter group P faced ex-Fenway P faced at Fenway P faced ex-Fenway P faced at Fenway
LHH 4th quartile 0.042 0.046 0.334 0.331
LHH 1st quartile 0.041 0.046 0.335 0.332
Difference 0.001 0.001 -0.001 -0.001
Batter group P faced ex-Fenway P faced at Fenway P faced ex-Fenway P faced at Fenway
RHH 4th quartile 0.041 0.043 0.323 0.329
RHH 1st quartile 0.041 0.043 0.324 0.330
Difference -0.001 0.001 -0.001 -0.001
SABERSEMINAR 2015 @BLABABOUTBALL