The average speed of a baseball varies greatly according to the circumstances. The speed of a ball after it is hit depends on the weight of the bat and the momentum of the swing. The average speed of pitched balls depends on the type pitch, including fast balls and curve balls, and the pitcher.
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Batted Ball Velocity
Assuming that for each pitch the same size ball is used and the pitch speed and swing speed are the same, a batted ball will have a faster velocity with a heavier bat. For his article titled "Bat Weight, Swing Speed and Ball Velocity," PennState professor Daniel A. Russell relied in part on "Physics of Sports," a high school textbook developed by Florida State University in 1980. That text reported results of experiments to test the speed of baseballs when the baseball mass, swing speed and pitch speed were kept constant. The study found that a bat weighing 20 ounces produced a batted ball velocity of 68.5 mph, while a 40-ounce bat produced a velocity of 80.4 mph. When the bat weight is kept constant, it's the speed of the swing that makes the difference. A swing of 20.5 mph produces a baseball speed of 62.0 mph. A swing of 47.9 mph produces a baseball speed of 91.4 mph.
Average Speed of Pitches
The speed of pitches depends greatly on the type of pitch that's thrown. According to measurements -- taken by eFastball's editor using a radar gun -- of pitches as they left the pitchers' hands, college and pro players' fastballs were typically thrown at an initial speed of 80 to 95 mph. In contrast, the speeds of a change-up pitch and a slider were about 70 to 85 mph. The speed of a curveball was about 65 to 80 mph and a knuckleball's speed was about 55 to 70 mph.
Fastest Pitches Recorded
Of course, the skill of the pitcher determines the speed of any pitched ball. According to "Popular Mechanics," the "Guinness Book of World Records," which accepts only speeds clocked by certified radar guns, lists Nolan Ryan's 1974 pitch of 100.9 mph as the fastest. However, Major League Baseball has recorded even faster pitches. Another pitch by Ryan was clocked at 108 mph. One of Ryan's fellow Hall of Famers, the late Bob Feller, pitched a ball at 107.6 mph, and Aroldis Chapman, a pitcher with the Cincinnatti Reds as of the date of publication, has recorded a 105.1 mph toss.
Young Players and Pitches
The average pitch speed among 14-year-olds would be about 65 mph, according to Steven Ellis, a former pitcher for the Chicago Cubs. Ellis stated that the average pitching speed required for a 14- to 15-year-old to make a good prospect for a junior varsity-level high school baseball team would be about 75 mph.