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- Cochems, Eddie, "The Forward Pass and On-Side Kick", Spalding's How to Play Foot Ball, American Sports Publishing, Walter Camp, Editor, Revised 1907 edition
- "What is Spiral? Definition from SportingCharts.com". sportingcharts.com.
- Chad Orzel. "Football Physics: Why Throw A Spiral?". Forbes.
- "A course in football for players and coaches".
- David M. Nelson. The Anatomy of a Game: Football, the Rules, and the Men who Made the Game. p. 53.
- Mark F. Bernstein. Princeton Football. p. 14.