In each of the past two seasons, I have published articles examining how bettors could find value by taking overs at Coors Field in Denver, Colorado. The Rockies home ballpark is famous for being the most hitter-friendly stadium in baseball, and the main reason for these high-scoring games and lofty totals is the thin air in Denver.
Weather conditions are an important influence on the trajectory of a baseball with air pressure, wind, temperature and humidity all considered significant factors. For example, my research found that MLB overs have gone 2,451-2,255 (52.1%) when the wind is blowing straight out to centerfield since the start of the 2005 season. However, any system involving Coors Field totals starts with a conversation about air pressure.
You may already know that high altitudes create lower air density, but you may not realize the full impact of the mile-high air in Denver. Due to the reduced drag created by thin air, the ball travels significantly farther at Coors Field than it does at other stadiums. According to most studies, the baseball travels roughly 5% farther than at Coors Field as compared to ballparks located at sea level.
Fans may realize that hitters benefit from the mile-high air, but they may not realize how lower air density adversely affects pitchers — specifically their breaking balls. According to Richard Lee from diamondkinetics.com:
A curveball, thrown with topspin, creates a higher pressure zone on top of the ball, which deflects the ball downward in flight. Instead of counteracting gravity, the curveball adds additional downward force, thereby gives the ball an exaggerated drop in flight.
A fastball, on the other hand, travels through the air with backspin, which creates a higher pressure zone in the air ahead of and under the baseball. The baseball’s raised seams augment the ball’s ability to develop a boundary layer and therefore a greater differential of pressure between the upper and lower zones.
The effect of gravity is partially counteracted as the ball rides on and into increased pressure. Thus the fastball falls less than a ball thrown without spin (neglecting knuckleball effects) during the 60 feet 6 inches it travels to home plate.
When a baseball is spinning, it experiences the Magus force. This is what causes it to curve away from its initial flight path. However, the lower air density at Coors Field leads to a reduction in the Magnus force and therefore less break on certain pitchers including the curveball. In fact, a curveball is said to break approximately 20% less in Colorado as opposed to a ballpark located at sea level.
Based on this information, I believed there would be tremendous value taking the over in games played at Coors Field. My research found that although the Rockies were the seventh most profitable “over” team since the start of the season, there was an incredible split between home and away games.
- Rockies overs on the road: 418-482 (46.4%)
- Rockies overs at home: 493-419 (54.1%)
This development was nothing short of incredible as the Rockies were the league’s most profitable over team when playing at home, but the second-worst over team when playing on the road. Despite these impressive results, I was certain that additional filters could be applied to maximize the profits. Air expands as it warms up, so I surmised that the ball would travel further and overs would be more profitable during the summer months.
A quick search revealed that June, July, August and September have historically had the highest average temperatures in Denver, and I anticipated that these would be the most profitable months for betting Coors Field overs. Sure enough, in these sweltering months the over has won at a 55% clip over the past eleven seasons.
Warm weather and lower air density have clearly led to high-scoring games and profitable returns for over bettors, but I believed this edge would be magnified in late season games due to pitcher fatigue. By focusing solely on games played in August and September, the winning percentage leaped from 55.0% to 60.7%.
Historically there has been more value betting overs when there’s a low total, and more value betting unders when there’s a high total. Typically we would categorize a closing total of 8 or less as “low” and 8.5 or more as “high.” Unfortunately, conventional logic doesn’t always apply to games played at Coors Field.
Since 2005, only 2.5% of all games played at Coors Field (23 of 912) have featured a closing total of 8 or less. Based on that data, I wanted to examine the performance of Coors Field overs based on the closing total.
|Closing Total||Over Record||Win Rate||Units Won||ROI|
|8 or less||14-9||60.9%||+4.13||18.0%|
|8.5 or less||45-26||63.4%||+15.52||21.9%|
|9 or less||102-77||57.0%||+19.16||10.7%|
|9.5 or less||213-171||55.5%||+31.90||8.3%|
|10 or less||293-248||54.2%||+30.29||5.6%|
|10.5 or less||396-319||55.4%||+55.86||7.8%|
|11 or less||440-362||54.9%||+53.92||6.7%|
|11.5 or less||465-391||54.3%||+48.81||5.7%|
|12 or less||475-404||54.0%||+45.71||5.2%|
In terms of units won, the most profitable threshold for taking Coors Field overs is when the total is 10.5 or less. When we look at those “low totals” during August and September, we find that the over has gone 152-90 (62.8%) with +54.80 units won and an incredible 22.6% return on investment (ROI).
When building a data-driven betting system, I usually look for a large sample size, consistent year-to-year results, and a strong guiding philosophy. With nearly 250 past matches it clearly has a substantial sample size and our driving hypothesis is based on proven scientific findings. In terms of consistency, very few systems boast these type of routinely profitable returns.
It’s also worth noting that many of our contrarian philosophies can be applied to improve the expected returns of this betting system, albeit at the expense of sample size and overall units earned. The return on investment increases substantially when less than 50% of bettors are taking the over, or when the Rockies are the underdog. That makes sense because if the Rockies are favorites, they are more likely to win, which means they wouldn’t need their final at-bats in the bottom of the 9th inning.
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