Deriving MLB Betting Value from Weather and Climate

Rainman M.

Monday, August 7, 2017 1:03 PM UTC

Monday, Aug. 7, 2017 1:03 PM UTC

In deciding what games to bet on, bettors prioritize pitching and hitting statistics. Rightly so. But they tend to consider pitchers and hitters without considering the environment that they play in.

Bettors can gain an advantage over their bookies by understanding the significance of weather and climate.

Baseball is in many ways a game of inches.  A pitch barely misses its spot and the batter takes advantage by hitting a walk-off double. A batted ball travels and just makes it over the fence for a home run.  This article shows the role that weather and climate play in determining the meaning of those few inches. Because a few inches can make the difference between a win and a loss, bettors do well to gain every possible advantage. Weather and climate are two often understated but important factors in baseball handicapping. Those who are new to betting on baseball will find this information useful as a guide to deriving significance from location. Looking solely at a team’s or player’s road splits is rather meaningless because of the variety of ballparks in which he plays. This article aims to introduce new baseball bettors to the meaning of location by discussing the impact that weather and climate can have on a given game. More seasoned baseball bettors who already know certain trends, such as the positive correlation between higher temperature and home runs,  can still benefit by reading this article in order to gain at least a better understanding for the explanation of certain realities.

Certain pitches work better in certain environments. This is because pitches are to a considerable degree determined in their path and velocity by the external forces acting, or not acting, upon them. This reality is most obvious in Coors Field, Colorado. Colorado is known for its lack of altitude. Higher altitude means low air density, or thin air. Lack of air density is undesirable for pitchers who like to throw a curve ball, but desirable for hitters who swing for the fences. Lack of air density means less resistance for balls that hitters launch into the air, meaning that a fly ball has less force acting against it and deterring it from becoming a home run. The curveball relies on a similar kind of environmental resistance in order to break effectively. Because this environmental force is lacking in high-altitude environments, the curve ball seems doomed at Coors. The curve is not so much doomed as that it requires adjustment. The pitcher, knowing that his curve will drop less at Coors, can aim in a different spot in order to compensate for the lack of drop. Over time, pitchers can more or less adjust to throwing a curve in Coors. But pitchers who love to throw a curve ball and come to Coors as part of the visiting team are likely to be in trouble.

One case example would be Indians pitcher Trevor Bauer.  When he pitched in Coors on June 7th of this season, his curve dropped an average of 6.66 inches, when on the year it drops an average of 3.01 inches more. In that game, he lasted 3.1 innings and gave up 4 runs. The curve ball drops less in high-altitude Coors Field because high-altitude means low air density.  But altitude is not the only factor that reduces air density: humidity (water vapor in the environment) and higher temperature achieve the same effect. Air density is important wherever there is air—Coors is just a typically extreme example because of its high altitude. Wherever humidity, but also more especially temperature, are high, look for the air density to be low.  Low air density means that curve balls lose their effectivity, while power hitters gain an advantage.

Regarding hitting, the Rockies are notorious for their struggles on the road. At home, their OPS (on-base but slugging; average is around .730) is .870. On the road, it drops to .698. The reason for the struggles of the Rockies on the road is the huge difference in the kind of environment at Coors to other environments. The Rockies have to adjust from seeing less breaking pitches and pitches that break a lot less, to seeing pitches that break more. As a result, they swing and miss more often on the road because the level of break in pitches outside of Coors Field comes at a shock to them. This season, they have 530 K’s on the road, but 432 at home. The misjudgment of the ball’s vertical path inhibits batters from tracking the ball when they decide to swing at a pitch. So they track pitches better at Coors where the breaking of vertically-driven pitches like the curve and sinker (or similar pitches, like „fastballs“ that rely on sinking action) is mitigated. The curve drops less while its velocity increases. But, they struggle with this enhanced verticality on the road.

Learn how to use batted ball stats to find betting value

The pitch that, comparatively speaking, tends to work best at Coors is the four-seam fastball. Jhoulys Chacin pitched in Coors Field from 2009-2014, during which span he threw his four-seam fastball at a career high rate. The problem with his reliance on the fastball is that the fastball is not his best pitch. Chacin is not a power pitcher by nature, but a finesse pitcher who relies on a variety of breaking pitches. Chacin’s career numbers at Coors reflect his inability to adapt to its environment: his ERA in Coors is 4.21 in 61 starts.  In San Diego, however, he is a completely different pitcher. This season, he is throwing his fastball with less than half of the frequency than he did in Colorado.  In San Diego, his ERA is 2.14 in 14 starts. San Diego has a completely different environment than Colorado and it is completely conducive to a pitcher like Chacin.

If the Rockies were to go from a long home stand to facing Chacin on the road, betting on Chacin to throw a no-hitter would not be a bad idea. At sea level, where altitude is very low and air density is much higher, the ball will not travel as far nor be carried in the air as long because there is more resistance acting against the flight of the ball. Resistance against the flight of the ball is strongest in those stadiums that are closest to the Pacific Ocean: San Francisco, Oakland, San Diego, Seattle and Los Angeles (Dodgers and Angels). The proximity to the Pacific Ocean is important because of the „marine layer,“ which is an air mass that is cool because it derives from contact with the relatively low surface temperature of the Pacific Ocean, which is cooler than the Atlantic Ocean because it collects from the Gulf of Alaska. This air mass traps fly balls in the air. It is also more thicker because cold air molecules denser  than hotter air molecules. 

Teams that rely on home runs for their production will struggle close to the Pacific Ocean, particularly when the temperature is cool, because cooler temperature maintains the marine layer. When the weather is warm enough, the marine layer will disperse, and so day games closer to the Pacific Ocean will witness a significant uptake in scoring particularly when fly ball pitchers are on the mound and when hitters, like Todd Frazier, who tend to hit the ball up into the air, are in the lineup, because then the ball will fly out and carry more into the air more strongly and will more likely become a home run.  A pitcher like Chacin does not only benefit because less of his allowed fly balls carry into home runs, but because there is, in contrast to Colorado, more environmental resistance from which his breaking pitches (particularly the curve and sinker) derive the effectivity of their break. He is a more effective pitcher in San Diego because he is by nature a breaking ball pitcher and his pitches break more effectively in San Diego.

So, we talked about the general factors that reduce air density: altitude, higher temperature, and also humidity (water in the air).  Lower air density favors power hitters and hurts pitchers who rely on breaking pitches with vertical movement, like the curve and sinker. Two extreme examples were Coors Field in Colorado and PetCo Park in San Diego. But these factors are important to consider wherever air can be more or less dense. They not only impact pitchers and batters in a given game, but in ensuing games as players try to make adjustments while rotating from ballpark to ballpark.  Bettors who live near a ballpark would do well to go to that ballpark as one can consider additional stadium-specific factors. One thing to look for would be the correlation between a certain direction of the wind with the lowest average exit velocity of home run balls. This correlation indicates the specific direction of the wind that does the best job of carrying balls in a given ballpark. For instance, if a northerly wind in X stadium does the best job of carrying fly balls and is blowing heavily on a given game, then, in that game, this wind reduces the value of fly ball pitchers and increases that of fly ball hitters.
Oddsmakers and sportsbooks account for a park being hitter-friendly or pitcher-friendly, which is why the posted totals at Coors Field are so high. But oddsmakers do not account for the style of pitcher or the character of lineup.  For instance, the Rockies team total ‚over' had great value when Bauer came to Denver because of his reliance on the curve ball.  So value is derived from weather and climate in three steps: 1) understanding the importance of specific climate factors (such as high altitude in Coors), 2), assessing the kind of lineups (i.e. tends to rely on home runs) and pitchers (power or finesse) that are playing, and 3), predicting the interaction between the two.

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