  We investigated the release angle that maximises the distance attained in a
long soccer throw-in. One male soccer player performed maximum-effort throws
using release angles of between 10 and 60 degrees, and the throws were analysed
using 2-D video. The player's optimum release angle was calculated by
substituting mathematical expressions for the measured relations between
release speed, release height, and release angle into the equations for the
flight of a spherical projectile. We found that the musculoskeletal structure
of the player's body had a strong influence on the optimum release angle. When
using low release angles the player released the ball with a greater release
speed, and because the range of a projectile is strongly dependent on the
release speed, this bias toward low release angles reduced the optimum release
angle to about 30 degrees. Calculations showed that the distance of a throw may
be increased by a few metres by launching the ball with a fast backspin, but
the ball must be launched at a slightly lower release angle.
