Biomechanical Analysis of an AFL Set Shot: Introduction

In a sport that is rapidly evolving from what it used to be, the set shot in AFL is still one of the most predominantly used skills in the game. A poor set shot technique can often result in a player unable to consistently hold their spot in the team which can be especially demoralising for a key forward who is normally relied upon to kick set shot goals. A prime example of this is Travis Cloke from the Collingwood Football Club.

Cloke at the peak of his career was a premiership winning key position forward that scored goals for fun, yet a change in his kicking technique has resulted in a loss of confidence and he is now a shadow of his former self. This blog aims to identify the optimal technique for a set shot for goal by analysing the key biomechanics involved. This will be done through deconstructing the skill and focussing on 6 crucial elements of a successful set shot which include; the run up, the role of the non-kicking leg during the leg plant, the ball drop, the leg swing, ball contact and follow through.

Analysis

How does the run up affect the kick?

Increasing stability and increasing the force transferred to the ball are the two main biomechanical factors of the run up. Players who take 3 or more straight steps (not curved) prior to taking their set shot kick will balance themselves and their technique. Maintaining balance when kicking a football allows all of the energy being produced in the kinetic sequence to be brought together to produce a series of fast movements. It is also a lot easier to balance when you are moving rather than being stationary. This idea is also evident when riding a bike as it is much easier to stay balanced and stable on a bike when it is in motion compared to when it is stationary which is due to angular momentum when the bike is in motion (Blazevich, 2013). There is less of a need for heavy objects or person to be moving in a fast motion to create stability, but having some momentum prior to a kick is still useful for a playing having a set shot as it makes it easier for them to stay stable for the kick (Blazevich, 2013). Extra stability will improve the accuracy and consistency in a players kick as it results in better control of the ball drop and a straighter leg swing.

A greater momentum build up into the run up adds kinetic energy to the leg swing and the football.  Kinetic energy (KE) is the energy associated with motion; thus, an object that is moving faster has far greater kinetic energy (Blazevich, 2013). It is also important that the non-kicking foot is planted forward and well in front of the player’s hips. This allows for the players kicking leg to be left behind him at a greater angle and for the hips to rotate horizontally away from the kicking leg. Kinetic energy is produced as the hips rotate away from the kicking leg. Accuracy should not be compromised as the player’s trunk should remain relatively stable, upright and facing towards the target. These factors allow the kicking leg to produce a greater force that can be applied to the ball when it makes impact with the foot.

Why is the planting of the support leg important?

Figure shows elevated heel raise and toes pointing at the target

The support leg and foot plant provides a platform so that the kicking leg can swing through (Bell, 2013). It also supports the player by absorbing the force generated by the speed of the players run up. A well braced support foot means that an increased force can be generated in the kicking leg as it allows for the hips to rotate more towards the kicking side. For example of the foot of the support leg is turned outwards the rotation of the hips will be minimised. Evidence also suggests that a greater elevation of the heel (plantar flexion) of the support foot helps to increase accuracy and distance of the kick (Bell, 2013). This is due to an elevated heel pushing the body away from the ground (Newton’s Third Law) adding more vertical lift to the kicking foot which increases the force that is transferred to the football on impact. Having plantar flexion of the support foot also allows the kicking foot to be plantar flexed more. This means that the toe of the kicking foot can be pointed more towards the target which will allow for better accuracy in the kick. The plantar flexion of the support foot is related to Newton’s Third Law: for every action, there is an equal and opposite reaction (Blazevich, 2013). In this instance the ground exerts an equal and opposite reaction force called the ground reaction force (GRF), which stops the foot from just sinking into the ground (Blazevich, 2013). When the support foot plantar flexes during the kick it is exerting enough vertical and horizontal force that is equal and opposite of the GRF (Blazevich, 2013).

How does the ball drop influence the drop punt?

The ball transition from hand to foot during the kicking sequence has the ability to influence the distance and accuracy of the kick. The key to a successful ball drop is to control the flight of the ball after it leaves the hand and before it strikes the boot. When considering the ball drop and kicking action the truck position is vital and plays an important role in deciding the accuracy and distance of the kick. Guiding the ball and leaning forward and dropping the ball closer to the foot allows for more accuracy and control but inhibits full body movements which includes generating more leg speed (Millar, 2004). When kicking the ball with a backwards leaning trunk the ball will be dropped from higher position which decreases the control in the ball drop as the ball has more time to travel between the moment of the ball drop and the moment the ball has contact with the foot. Manipulating the body’s center of mass is essential in order to maintain balance during the set shot and it is recommended to release the ball around hip height to ensure the correct trunk position is in place while allowing for enough time for the ball to be guided from hand to foot which builds up impulse momentum allowing more time for the leg to extend out whilst maintaining balance (Blazevich, 2013). 

Figure shows former Brisbane Lions AFL player Daniel Bradshaw's set shot kicking action with the point of the ball making contact with firmest part of his foot (laces on his boots).

How to achieve a powerful and controlled leg swing

There are several key aspects during the leg swing movement phase that are critical order to maintain balance and achieve an ideal center of gravity when shooting for goal. Cameron and Adams (2003) state that the control of the swinging leg is only one factor of the kicking movement, and other kinematic and kinetic considerations may be more important determinants of kicking ability. Thigh muscle strength, efficiency of muscle contraction, support leg placement and body segment coordination have been linked to kicking performance. During the kicking movement, control of lower leg motion will be a factor in determining foot velocity, the quality of contact between the foot and ball, and ultimately the kicking performance (Cameron & Adams, 2003). During the leg swing phase in which the player moves their leg backwards from the front of the body they player must overcome the inertia of the leg (Blazevich, 2013).  In a rotational sense this can be seen as Newton’s First Law an object will remain at rest or continue to move with constant angular velocity as long as the net forces causing rotation equal zero (Blazevich, 2013).

In a study conducted on the kicking accuracy of elite footballers, Cameron and Adams (2003) aimed to identify the biomechanics involved in achieving distance and accuracy when kicking for goal. A noticeable variable was found in which some participants had a fast leg swing when kicking the ball, and some participants having a slow leg swing when kicking for goal. The results indicated that the subjects who had the slower swings also had the lowest foot angular velocities at foot-to-ball contact. Interestingly, the two subjects who appeared to have the fast swings were known for the distance that they attain with their kicks and the two subjects who had the slower swings were more renowned for their accuracy.

How does the follow through affect kicking performance?

Figure shows the one handed ball drop effect

During a set shot for goal most players tend to drop the ball onto their foot with the same side hand as their kicking leg. For example a left foot kicker will drop the ball onto their foot with their left hand. By dropping the ball onto the foot with the one hand leads to the opposite hand coming away from the body which results in the hips rotating. The rotation of the hips translates kinetic energy onto the ball which helps increase the length of the kick. The amount of kinetic energy achieved during the ball and foot contact is also dependent on the length of the person’s leg and their leg mass. Providing all else is equal (e.g. leg length and leg mass), players who drop the ball onto their foot using both hands (e.g. Warwick Capper) will have minimal rotation of their hips.  Therefore, they will reduce their kinetic energy that translates onto the ball and will result in having a shorter distance on their kick.

How does the ball contact with the foot effect kicking performance?

When having a set shot for goal or just kicking a drop punt in general, the players aim is to project the ball accurately over the desired distance at the desired velocity. It is important to note that the kicking action requires a series of linked segments including the thigh, shank and foot that extend sequentially to create a throw-like movement. The nature of the body means that these segments do not work in isolation, they combine in a series of segmental interactions that enable the required velocity of the striking mass to be obtained (Putnam, 1991). The moment in which the ball makes contact with the kicking foot is when the velocity and trajectory of the kicking limb is established and the trajectory of the ball is determined (Dichiera, 2006). For a player to achieve the desired velocity and distance, the kick is heavily reliant on the magnitude and direction of force imparted to the ball by the foot at the moment of contact. The force created at the moment of contact is a product of foot velocity and the quality of contact between the foot and ball. A strong relationship exists between foot and ball speed, and the subsequent distance of the kick. Foot velocity is determined by correct proximal to distal segmental motion of the leg, and control of lower leg motion directly affects foot speed. In addition, the point of and type of foot contact with the ball will influence the force applied to the ball. The location of impact in relation to both foot and ball, combined with the degree of foot stiffness and the direction of leg swing as well as the control of the swinging lower leg all affects the overall performance of the drop punt kick. (Cameron& Adams, 2003).  As the hip angular velocity of the preferred leg decreases toward the point of ball contact while the pelvis angular velocity continues to increase, the pelvis can be used to generate more power at the foot-to-ball contact. As such, rather than a larger hip extension, the larger last stride might be related to a greater pelvis range of motion which in turn leads to a larger pelvis angular velocity at ball contact (Falloon, 2010). When considering the leg position at foot-to-ball contact, the knee must not be fully extended, but should have a flexion of approximately 30-50 degrees and must continue to extend after contact (Millar, 2004).

In a study by Dichiera (2006) comparing the kinematics involved between accurate and inaccurate drop punts to a stationary target, the accurate group displayed a greater hip-flexion throughout the kicking movement, beginning with the hip in a slightly flexed position (2.6  degrees) whereas the inaccurate group began with the hip in an extended position (-12.1 degrees).  The results for ball contact when hip flexion was maximal also showed a significant difference between the accurate and inaccurate kicks. For the support limb, the hip began in flexion and decreased to nearly neutral at ball contact in both groups. Again the accurate group had a significantly greater hip flexion at heel-to-ground contact.

Why is the drop punt the most effective method of kicking in Australian Rules Football?

Jack Riewoldt swings his leg backwards during the first phase of the kick. This represents a throw like movement as his leg extends g sequentially. His hips also extend while his knee is still flexing during the back swing phase which creates an increase in the velocity of his ankle. This means that there will be a greater velocity during the ball and foot impact. Extending the leg back also produces a greater range of motion and as it creates low inertia and the inertia force in this case is Jack Riewoldt’s foot. This next phase involves Jack Riewoldt’s kicking leg be straightened out, with all the joints locked, creating a push like movement when the ball makes contact with the foot. Notice the hip, knee and ankle of Jack Riewoldt being aligned in a single straight movement which allows for the kick to have better accuracy. Once the ball makes contact with the foot it is then considered to be kicked and it will stay in motion with the same velocity (speed and direction) unless acted upon by another force (Newton’s First Law of motion) which in this case would be air resistance, wind, friction, gravity or a player or an object stopping it (Blazevich, 2013). As Jack Riewoldt performs a drop punt by starting with a throw like motion and then goes into a push like action he allows himself to kick the ball accurately and with a high velocity.

Figure from Blazevich (2013) shows the backswing to foot-ball contact kicking phases.

Conclusion

This blog has been created in order to give amateur footballers, coaches and teachers alike a basic understanding of the optimal biomechanical process involved in the set shot kick for goal in Australian Rules Football. Through breaking down the set shot for goal we have identified that the drop punt kick is ideal method for achieving an accurate shot at goal while also achieving great distance with the kick. Through the analysis of the run up, the role of the supporting leg, the ball drop, the leg swing, ball contact and the follow through we have discovered that by optimizing the timing of the rotation of the thigh in relation to the shank, increasing the angular velocity of the thigh and maintaining a maximum position of ankle plantar flexion throughout foot-to-ball contact are the key focus points from a coaches perspective to improve accuracy and distance in the set shot for goal.

By Corey Phillis and Lachlan Smith

References

Ball, K. (2013). Loading and performance of the support leg in kicking. Journal of Science and Medicine in Sport, 16(5), 455-459.

Blazevich, A. J. (2013). Sports biomechanics: the basics: optimising human performance. A&C Black.

Cameron, M., & Adams, R. (2003). Kicking footedness and movement discrimination by elite Australian Rules footballers. Journal of Science and Medicine in Sport, 6(3), 266-274.

Dichiera, A., Webster, K. E., Kuilboer, L., Morris, M. E., Bach, T. M., & Feller, J. A. (2006). Kinematic patterns associated with accuracy of the drop punt kick in Australian Football. Journal of Science and Medicine in Sport, 9(4), 292-298.

Falloon, J., Ball, K., MacMahon, C., & Taylor, S. B. (2010). Coordination patterns of preferred and non-preferred kicking of the drop punt kick: a kinematic analysis of the pelvis, hip and knee.

Millar, J. S. (2004). Kinematics of drop punt kicking in Australian rules football-comparison of skilled and less skilled kicking (Doctoral dissertation, Victoria University).

Parkin, D., Smith, R. and Schokman, P. (1987) Premiership football; how to coach, train and play Australian football. Hargreen, Melbourne.

Putnam, C. A. (1991) A segment interaction analysis of proximal -to- distal sequential segment motion patterns. Medicine and Science in Sports and Exercise, 23, 130 - 144.