keyboard_arrow_uptop

One of the first axioms I learned when I wandered into the world of sports betting was to heed Wrigley Field’s winds. Wrigley’s proximity to Lake Michigan gave it a reputation for dramatically affecting fly balls, which would inflate or deflate the game over/under on runs. If the wind was blowing out, fly balls were expected to sail out as home runs, and the total would be unusually high. A low total typically meant that winds were blowing toward home plate, suppressing fly balls.

Vegas already knew this, which unfortunately added an additional dimension to handicapping Cubs home games. Amazingly though, this advice was extremely exploitable in fantasy baseball. An “@ChC” note next to my pitcher meant a trip to Baseball Weather Analyzer or Daily Baseball Data (two sweet resources) to examine Wrigley Field’s conditions that day. Flyball pitchers sat on blow-out days and started on blow-in days.

Chris Constancio of The Hardball Times investigated the effect of winds on HR/FB rates six years ago, and he observed statistically significant results in Chicago parks. I replicated his method on data from 2007 to the present and found that the Wrigley wind effect is stronger than ever. Over 508 games, here’s how pitchers performed in HR/FB rate, ERA, and slugging percentage allowed, split by Retrosheet’s wind field:

Direction

Definition

Freq.

HR/FB%

ERA

oppSLG

In

Blowing In, 10+ mph

18.9%

8.9

3.47

.364

Still

Any direction 0-3 mph.

7.3%

16.7

4.17

.411

Out

Blowing Out, 10+ mph

10.0%

19.4

5.84

.508

Other

Any 4-9 mph, and cross winds

63.9%

12.7

4.24

.412

Harry Pavlidis, one of BP’s many Cubs experts, notes that wind direction and speed can change within a game at Wrigley Field.

Unfolding “Other” into its respective “In” and “Out” bins yields an intuitive symmetry, indicative of Wrigley’s varying wind spells:

Direction

Definition

Freq.

HR/FB%

ERA

oppSLG

In

In, 10+ mph

18.9%

8.9

3.47

.364

In, weak

In, 4-9 mph

28.9%

11

4.00

.397

Still

Any direction 0-3 mph.

7.3%

16.7

4.17

.411

Out, weak

Out, 4-9 mph

12.0%

16.3

4.96

.460

Out

Out, 10+ mph.

10.0%

19.4

5.84

.508

Cross

LF to RF, or RF to LF

22.8%

12.8

4.16

.405

The distribution of wind events is not perfectly uniform from season to season, but even when divided into yearly buckets (so that talent is better controlled for), the outcomes are very apparent.

A considerable portion of the performance of pitchers in Wrigley was affected by the day’s wind condition. I retrieved the splits for starters with at least 45 innings pitched each in the “In” and “Out” states at Wrigley, since 1998:

 

HR/FB%

ERA

oppSLG

Name

In

Out

In

Out

In

Out

Carlos Zambrano

7.4

16.2

3.19

3.42

.320

.370

Kerry Wood

9.0

23.0

2.63

4.67

.288

.441

Ryan Dempster

11.7

24.4

3.06

7.39

.349

.502

Jon Lieber

11.4

26.7

2.85

4.57

.323

.440

Kevin Tapani

19.4

18.8

3.47

5.38

.364

.490

Ted Lilly

7.9

19.7

2.12

5.80

.297

.563

Greg Maddux

14.9

24.1

3.39

4.20

.396

.462

Matt Clement

15.0

30.0

2.32

4.14

.285

.396

Mark Prior

5.8

22.1

2.32

5.14

.289

.502

No one was immune—not even The Professor. The effect is quite evident for starters with flyball tendencies like Wood, Lieber, and Lilly. Ultimately, the opposing wind extremes end up balancing each other out; taking the sum of all Wrigley Field numbers, the given rates are a sliver off league averages. However, the extremes might cause Wrigley pitchers to have more variation in their starts than a non-Wrigley pitcher.

The biggest beneficiary of the wind effect this season is Travis Wood. His 2.24 ERA ranks seventh in the NL, and every one of his nine starts has been deemed “quality.” Unsurprisingly, none of his six home starts featured a game with wind blowing in from the ivy:

Date

Wind

Speed

PA

AB

IP

H

R

ER

BB

SO

TB

HR

FB

20130409

In From LF

23

29

26

6.3

7

3

2

3

6

9

0

5

20130416

In From RF

5

28

24

7.3

5

2

2

3

3

7

0

6

20130502

In From CF

19

27

26

7.7

4

3

3

1

3

4

0

6

20130507

Still

2

28

26

6.7

6

1

1

2

8

10

1

3

20130513

RF to LF

5

24

21

7

2

0

0

3

2

2

0

11

20130519

In From RF

9

27

25

7

5

3

3

2

3

9

1

6

The “wind schedule” has skewed favorably for Wood in these early months. Combined with some BABIP luck, he’s evaded the regression that is looming—so far. We know he can’t sustain a .193 BABIP forever. But if he continues to serendipitously find the wind behind him, there’s a chance that his HR/FB rate will keep floating around his current 6.5 percent mark, enabling him to outperform his peripherals. For his career pitching at Wrigley, Wood’s numbers reveal a massive dichotomy:

Direction

IP

HR

FB

ERA

SLG

In

46

1

39

2.54

.247

Other

63.7

5

64

3.67

.346

Out

16.3

10

25

9.39

.818

Travis Wood is a flyball pitcher like Kerry Wood before him, and the wind effect on his numbers is amplified. Hitters won’t continue slugging .818 against him with southwest winds, but if the trend is real, the .508 opponent slugging mark served by Wrigley pitchers under those circumstances in the past seven years can be expected.

Obviously, the Cubs can’t control Mother Nature, nor schedule its starters around her. Pitchers at Wrigley Field will always be, to a degree, at the mercy of its winds. The fiercest months—April and May—are nearly over, but the summer games will still see the occasional gusty afternoon. It’s a convincing reason to observe the weather, whether you’re debating a start/sit decision for a fantasy starter, or you’re the Cubs manager, pondering your offensive strategy. 

You need to be logged in to comment. Login or Subscribe
jfranco77
5/22
Great analysis. And one more thing I have to check before I set my lineups.
AndrewKoo
5/22
Thanks! The two links I mentioned are really useful.
onegameref
5/23
Travis seems pretty athletic regardless of the wind. He can put the bat on the ball and runs better than your average pitcher from what I've seen. I like his potential in the long-term.
Cronfordox
5/29
daily baseball data!!!!!.....how did i live before you showed me this site?????