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The term knuckleball in sporting jargon is used to describe a ball that has been launched with minimal spin, resulting in a trajectory that is erratic and unpredictable. This phenomenon was first observed in baseball (where the term originated) and has since been observed in other sports. While knuckleball has long fascinated the scientific community, the bulk of research has primarily focused on knuckleball as it occurs in baseball. Following the changes in the design of the soccer ball after the 2006 World Cup, knuckleball and ball aerodynamics were exploited by soccer players. This research examined the properties of a knuckleball in the sport of soccer. We designed and evaluated a system that could reproduce the knuckleball effect on soccer balls based on previous theories and characteristics outlined in our literature review. Our system is comprised of the Adidas miCoach Smart Ball, a companion smart phone app for data collection, a ball-launching machine with programmable functions, and a video-based tracking system and Tracker motion analysis software. The results from the testing showed that our system was successfully able to produce knuckleball behaviour on the football in a highly consistent manner. This verified the dynamic models of knuckleball that we outline. While a small portion of the data showed some lateral deviations (zig-zag trajectory), this erratic and unpredictable trajectory was much smaller in magnitude when compared to examples seen in professional games. The sensor data from the miCoach app and trajectory data from the Tracker motion analysis software, showed that the knuckleballs were consistently reproduced in-line with theoretical dynamics. [ABSTRACT FROM AUTHOR]

The term knuckleball in sporting jargon is used to describe a ball that has been launched with minimal spin, resulting in a trajectory that is erratic and unpredictable. This phenomenon was first observed in baseball (where the term originated) and has since been observed in other sports. While knuckleball has long fascinated the scientific community, the bulk of research has primarily focused on knuckleball as it occurs in baseball. Following the changes in the design of the soccer ball after the 2006 World Cup, knuckleball and ball aerodynamics were exploited by soccer players. This research examined the properties of a knuckleball in the sport of soccer. We designed and evaluated a system that could reproduce the knuckleball effect on soccer balls based on previous theories and characteristics outlined in our literature review. Our system is comprised of the Adidas miCoach Smart Ball, a companion smart phone app for data collection, a ball-launching machine with programmable functions, and a video-based tracking system and Tracker motion analysis software. The results from the testing showed that our system was successfully able to produce knuckleball behaviour on the football in a highly consistent manner. This verified the dynamic models of knuckleball that we outline. While a small portion of the data showed some lateral deviations (zig-zag trajectory), this erratic and unpredictable trajectory was much smaller in magnitude when compared to examples seen in professional games. The sensor data from the miCoach app and trajectory data from the Tracker motion analysis software, showed that the knuckleballs were consistently reproduced in-line with theoretical dynamics.

The aerodynamic forces acting on a baseball are those produced by the contact between the ball and the air, and are defined by the initial conditions of the pitch. It is well known that such forces determine the changes from the typical parabolic ballistic trajectory, either in the direction of the movement of the ball (drag force), or producing a lift or lateral deflection (Magnus and seam forces). The drag and Magnus effects have been widely studied and there are many references about their nature and the trajectory they produce, which is predictable. This has led to most baseball research being related with spinning pitches. On the other hand, there is the unpredictable motion of a knuckleball, whose erratic trajectory accompanied by a poor understanding of the forces produced by the asymmetry of the seams had markedly limited research about it until the beginning of this century. However, nowadays interest in the knuckleball is resurfacing. Data collected by wind tunnel experiments and real pitches have motivated researchers to analyze the phenomenon and build models that try to predict the motion of the ball. In this work we aim to provide the reader some basic ideas on aerodynamic forces through a combination of experimental results, phenomenological and dimensional analysis, with special focus on new advances on the seam effects of a knuckleball pitch. In addition, we discuss possible ways to extend the existing models about the seam forces. Finally, we summarize from the literature some methods regarding the reproduction and reconstruction of baseball trajectories from aerodynamic forces and discuss their application as well.

The movement of a knuckleball depends on the seams of the baseball strongly, as a consequence a lift force proportional to the square of the ball velocity is occasioned. In this work we develop a model as a function of the position of the seams to compute the lift coefficient that appears in the lift force acting in upward direction, for four-seam (4S) and two-seam (2S) orientations of the ball. The result of the model is consistent with experimental data. In addition, deviations caused by lift force are calculated for all angles in the 4S and 2S orientations and some trajectories are generated. [ABSTRACT FROM AUTHOR]

Abstract: An analysis of knuckleball trajectories is presented using data from the PITCHf/x video tracking system for pitches thrown in actual MLB games. The data reveal that, contrary to popular belief, knuckleball trajectories are as smooth as those from normal pitches. However, the data also show that the deflection of a knuckleball from a straight-line trajectory is essentially random in both magnitude and direction. [Copyright &y& Elsevier]

The purpose of this study was to discuss the fluid mechanics acting on a non-spinning and low-spinning flight soccer ball, which called "Knuckling effect ball"or "Knuckleball", using the kick-robot. This robot is driven by high-pressure air in an air cylinder up to 500 kPa, being capable of generating a ball flight up to about 30 m/s. The machine with a size of 1.8 m x 2.5 m x 2.0 m in height can be moved, and be set both inside of a gymnasium and outdoor field. The ball speed can be set between 10 m/s and 30 m/s. Some condition of ball hitting can be adjusted, such as the hitting speed for the ball flight speed, the contact angle between the hitting-board and a ball for the shot angle and the off-axis distance between the normal line to the hitting board and the ball center for the ball spin rate. It is planned to conduct experiments on the knuckle effect of a non- or low-spinning soccer ball. It was determined that the peak of the irregular force in this experiment was about 2.1 N (s.d.=0.4 N). Furthermore, the knuckleball was observed to have an average lift force frequency of approximately 2.0 Hz. It can be concluded that the emergence of irregular forces is one of the characteristics of knuckle balls in soccer. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study is to analyze the swing characteristics of the kicking leg in order to elucidate the technical mechanisms of the knuckling shot. The tendency to impact with the heel pushed out towards the inside of the foot was considered. Hip external rotations in the knuckling shot exerted greater external rotation torque of the hip joint than the other shots. In this manner, it can be considered that compared to the other shots, the knuckling shot exerts a greater external rotation torque on the hip and has a tendency to impact with the heel pushed towards the inside of the foot. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to analyze the fluid mechanics and frequency of forces acting on a knuckleball, specifically a soccer ball that was kicked and was in flight, was visualized using a smoke agent (titanium tetrachloride), and its unsteady aerodynamics were investigated. In the case of the knuckleball, the peak value of the vortex lift reached approximately 2.0 N, and the average vortex lift force frequency of approximately 3.5 Hz. A comparison of this vortex lift frequency and vortex oscillation frequency indicated that these frequencies tended to act in unison with a high statistical correlation . [Copyright &y& Elsevier]