Mathematics of hitting a home run

Summary: Home runs in baseball can be mathematically analyzed according to numerous factors, including ballpark design, altitude, and initial velocity.

A home run in baseball happens when the batter circles all the bases in a single play. This typically results from the ball being hit over the outfield fence. In modern baseball, a home run rarely occurs as a result of hitting the ball so that it is still in a state of play inside the field—an “inside the park” home run. Home runs are considered to be some of the most exciting plays in baseball, and a great deal of time and effort is spent trying to help batters achieve this skill.

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A number of factors are at work in hitting a home run, including the player’s stance and swing, the flight path of the ball, and the characteristics of the outfield wall, which are not standardized in U.S. baseball stadiums. For example, the Boston Red Sox stadium is renowned for its left field wall, named “The Green Monster,” which is much taller than average outfield walls, but it is only a little more than 300 feet from home plate—a fairly short distance in professional baseball. Probability and statistics are also used to analyze home runs, though differences in the game over time make some mathematical comparisons challenging. The 1961 race between Roger Maris and Mickey Mantle to break George Herman “Babe” Ruth’s home run record was widely followed and highly controversial, in part because the increased number of games in the season made direct comparisons of the number and rate of home runs problematic.

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There are various techniques, training schools, and methods to improve a batter’s chances of hitting a home run. Contributing factors considered in some of these methods include the mass of the baseball bat and the speed at which the bat is swung. A projectile equation is used to model the motion of the ball as a parabola, using these variables as input. The distance traveled and the greatest height achieved both depend on initial conditions starting from when the ball hits the bat: height, angle, velocity in units of distance per second, and other factors such as altitude above sea level. There is also a great deal of research in sports medicine and kinematics. Some of this research focuses on batter and performance variables, such as age, bat grip, bat speed and velocity, reaction time, and visual cues, though the fundamental mathematical analyses of trajectory do not differ.

Mathematicians and scientists have also developed computer simulations designed to model batting. These often allow multiple parameters to be modified dynamically and quickly to explore and to visualize results. One such simulator shows that when a batter hits a baseball, the air resistance, speed, and angle all have an effect on where the ball goes. It further allows the user to choose a stadium location and then alter the speed, angle, and altitude to observe the success or the failure.

Baseball statistics may be more familiar to the wider sports audience, from the numbers that appear on the backs of baseball cards to the advanced mathematical analyses of sabermetrics. For example, in September 2007, four Los Angeles Dodgers players hit four home runs in a row. This was only the fourth time this had ever happened in over a century of major-league baseball. A sports-business professor calculated the odds as 1:3,300,000, a number that gained wide attention in the media.

Then, roughly a month later, four Boston Red Sox players repeated the exceptionally rare feat, spurring alternative calculations and discussions among statisticians and sports analysts. Mathematician Howard Penn used statistical hypothesis testing to determine whether the Colorado Rockies’ practice of humidifying their baseballs (to counter the beneficial effects of high altitude on distance), actually reduced their overall number of home runs. He concluded that there was a statistically significant decrease, though the park was still “home run friendly.”

Bibliography

Adair, R. K. Physics of Baseball. 3rd ed. New York: HarperCollins, 2002.

Bertoletti, John, and Rhea Stewart. How Baseball Managers Use Math. New York: Chelsea House Publications, 2009.

Penn, Howard. “Did Humidifying the Baseball Decrease the Number of Homers at Coors Field?” Mathematics Awareness Month (April 2010). http://mathaware.org/mam/2010/essays/PennBaseball.pdf.