Enjoy the game. The Rule 35 Hat pays homage to Callaway’s first ever golf ball, Rule 35. Released in 2000, the Callaway Rule 35 golf ball marked the company’s innovative entry into the ball market. At the time, “Rule 35” was Callaway’s fictional addition to the official 34 rules of golf: Enjoy the Game. This limited edition collection brings the iconic Rule 35 design back, adding a timeless style to your game.