Just like a knuckle ball in baseball, a knuckle for a soccer ball -- perfected by Real Madrid’s Cristiano Ronaldo -- creates a ball that moves erratically, making it tough for a goalkeeper to track and catch. The knuckled soccer ball may even zigzag, writes Helge Norstrud, a Norwegian professor of aerodynamics, in “Sports Aerodynamics.” Air flow becomes affected around the seams of the ball if it is kicked at a critical speed, such that it can suddenly dip as it arrives at the goal. Although an off-center kick creates strong sidespin for a banana kick, you reduce the amount of spin you apply to create a knuckle in soccer.
Practice your technique against a wall or rebounder to start. Run up to the ball and plant your support foot normally.
Kick the ball with the area on top of the foot, slightly to the inside, and not far from the ankle joint. Land on the kicking foot in front of where the ball was. Collect the ball after it rebounds and continue practicing the knuckle kick.
Stand outdoors about 25 yards from a full-size goal. Focus on your technique rather than the target, recommends Steve Roberts of STR Sports Coaching, based in Suffolk, England.
Kick the ball with very little follow-through, swinging your leg straight through the ball, rather than pulling the leg across your body. Aim above the target area, as the ball will dip into the net at the end of its trajectory.