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Bat design and ball exit velocity in baseball: Implications for player safety - page 11 / 12





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Velocity component

Metal (ms-1)

Wood (ms-1)


Bat tip (X)

37.46 ± 3.19

34.09 ± 3.86


Bat tip (Y)

1.09 ± 5.34

-2.69 ± 4.52


Bat tip (Z)

8.70 ± 5.74

6.81 ± 8.05


Bat tip (resultant)

39.39 ± 3.24

36.39 ± 3.25


an angle between the global z-axis, axis of rotation and the bat tip, projected on the XZ plane (Figure 1). The tip of the wood bat was typically located 22 degrees behind the horizontal position achieved by the metal bat 0.005 s prior to impact. The greater angle of incidence and reflection during the bat-ball impact may have resulted in decreased ball exit velocity from wood bats due to greater frictional force.

Table 2: Instantaneous bat tip linear velocity (m/s) for wood and metal baseball bats (0.005 s prior to ball contact)

  • *

    p < 0.01

Cassidy and Burton (1989) indicated 400 ms is required for a pitcher to complete a reactive movement to avoid being struck by the batted ball. This corresponds to a ball exit velocity of approximately 42 m/s. Mean ball exit velocity from wood bats in this study (Table 4) was 40.8 m/s. This finding supports the use of wood bat exit velocities as a “gold standard” to determine permissible bat performance in baseball. On July 19, 1999, the US National Collegiate Athletic Association (NCAA) Baseball Rules Committee ruled ball exit velocity of 93 ± 1 mph (41.57 m/s) was the certifiable limit for all metal bats used in college baseball. This ruling was based on BBV tests conducted on solid wood bats, considered an acceptable standard as they have been in use since the inception of the game. Our results suggest ball exit velocity from wood bats swung by live hitters is within, but at the upper limit of, human reaction time for defensive players. The finding that average exit velocity from metal bats was 43.98 m/s (98.95 mph), and as high as 120.97 mph, indicates a high potential for impact injury to fielding players.

Table 3: Bat orientation (deg) at the instant 0.005 s prior to ball contact for wood and metal baseball bats.


Metal (deg)

Wood (deg)



120.53 ± 3.59

118.57 ± 7.26



359.37 ± 13.93

338.89 ± 7.66


  • *

    p < 0.01

The velocity of approximately 11% of all linedrives from metal bats exceeded 49 m/s, ranging up to a maximum ball exit velocity of 54.077 m/s. This value is approximately 5 m/s greater than the maximum velocity achieved from the wood bat (49.115 m/s). However, a maximum BBV of 49.17 m/s from wood bats was recorded, which again exceeds the recommended safe limit by 8 m/s (17 mph). This finding is substantiated by the April 8, 2001 injury to Cleveland Indians’ pitcher Steve Woodard, struck and injured by a linedrive from a wood bat during the first week of Major League competition. Houston relief pitcher Billy Wagner was hit in the head by a line drive on July 16, 1998 - a blow from which the ball caromed into the third-base dugout (Baum, 1998). Such incidents indicate the issue of equipment design and safety in baseball may extend beyond bats to factors including the elastic properties of the ball, the dynamics of the impact between bat and ball, increasing size and strength of hitters, the distance of the pitcher from the batter and protective equipment for defensive players.

Table 4: Mean ball exit velocity (m/s) for wood and metal baseball bats (0.01 s after ball contact).

Bat Metal Wood

Mean ball exit velocity (ms-1)

    • 43.98

      ± 4.95

    • 40.80

      ± 4.30

p 0.0257

CONCLUSIONS: A clear relationship exists between bat weight distribution and both the orientation and linear velocity of the bat at impact. This has important implications for ball exit velocity and player safety. Reversion to exclusive use of wood bats is not an economically viable solution for non-professional baseball leagues. Current NCAA regulations for metal bats in collegiate play legislate for design features including maximum bat diameter and length-to-weight ratio. All bats must also conform to a maximum BBV of 93 +/- 1 mph when swung at 80 mph by the Baum Hitting Machine. Although specific to these bats and players, the results of this study clearly indicate a certified bat swung by a live hitter may produce BBV exceeding that demonstrated when using the Baum Hitting Machine. On June 12, 1999, the NCAA Baseball Rules Committee announced recommendations that mass distribution regulations be adopted for metal bats, although this legislation remains to be enacted. The results of this research support such recommendations.


1. 2. 3. 4.

“Researchers release latest catastrophic-injury report” NCAA News June 8, 1998 Adair, R.K. (1994) The Physics of Baseball 2nd edition. Harper Collins, New York Ashley, S. (1991) Wood-composite baseball bats take the field. Mechanical Engineering August 1991: 43-45.

















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