This constant represents the height of the crossbar of the standard goal post in American college football.

The goal post at each end of the football field is defined as follows in Article 5 of the 2015 NCAA Football Rules and Interpretations:

a. Each goal shall consist of two white or yellow uprights extending at least 30 feet above the ground with a connecting white or yellow horizontal crossbar, the top of which is 10 feet above the ground. The inside of the uprights and crossbar shall be in the same vertical plane as the inside edge of the end line. Each goal is out of bounds (see Appendix D).
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b.    Above the crossbar, the uprights shall be white or yellow and 18 feet, six inches apart inside to inside.
c.    The designated uprights and crossbar shall be free of decorative material (Exception: 4-inch-by-42-inch orange or red wind directional streamers at the top of the uprights are permitted).
d.    The height of the crossbar shall be measured from the top of each end of the crossbar to the ground directly below.

To compute the trajectory of a field goal attempt, the kicker is then targeting and area above the ground that is 18 feet wide, starts at 10 feet above the ground and extends (theoretically) upward to infinity. 

See also

• Ohio State vs Michigan Scores
• Football Calculator
• Aerodynamic Torque on a Football
• Deflection Due to Magnus Force
• Drag Force on a Football
• College Football Consensus National Champions Data
• Most College Championships
• Number of College Football Championships
• Goal Post Cross-bar Height (American Football)
• Length of Football Field
• Sport Ball Sizes
• Minimum Football Circumference - NCAA
• Minimum Football Length - NCAA
• Maximum Football Circumference - NCAA
• Maximum Football Length - NCAA
• Minimum Football axis_1 or axis_2 - NCAA
• Maximum Football axis_1 or axis_2 - NCAA