Introduction
This analysis will discuss the biomechanical principles involved in performing a drop punt in Australian Rules Football (AFL). A successful drop punt is crucial in the game of AFL. It is one of the main skills required to be successful and is also the hardest to learn for beginners to the sport with both the correction action and ball drop required to execute the skill. Successful execution of the drop punt requires many different biomechanical principles through each stage of the lead up, execution and follow through of the kick. A successful drop punt involves power, accuracy and correct direction of spin. As learners move from a cognitive learner to associative and finally autonomous, their kicking style and execution will dramatically change. It is vital for autonomous learners to be able to complete this skill in high pressure (game situations) and continuously complete the skill with minimal errors and minimal variance in technique and result.
Previous research into the biomechanics of kicking has been dominated by investigating the motion of the kicking limb. More specifically, research has focused on the kinematics of the forward swing. The kicking limb is not a single unit, rather a series of linked segments – thigh, shank and foot. This means that the 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 attained (Putnam, 1991).
Major Question
What are the basic biomechanical principles to consistently execute a successful AFL football drop punt?
Answer
Skill – Drop punt
Drop punt kicking is a complex movement that involves all the limbs of the body. The arms play a part in the drop of the ball and assist in balancing the body. The muscles of the trunk provide stability for the pelvis as the limbs rotate and the support leg is the weight bearing leg. Each kick has a sequence of events that have to occur to allow for successful execution of the skill. The phases and biomechanical principles involved in the execution of the drop punt include:
- Newton’s law
- Run up
- Planting of the support leg
- Ball drop
- Leg swing
- Contact
- Levers
- Ideal trajectory
- Follow through
(Figure 1. Sequence of drop punt)
Newton’s laws:
Newton’s 1st law states that all things at rest want to stay at rest (Blazevich, A., 2012).
How does the player apply force to bring the object (football) from rest to motion? A player brings the ball from rest to motion by running with the football and then dropping the ball onto their foot which drives back behind the body before swinging through towards the intended target and making contact with the ball. This force then moves the ball from rest into motion towards the direction and angle that force was applied.
Newton’s 2nd Law states that Force = Mass multiplied by acceleration (Blazevich, A., 2012).
Kicking a football over any distance requires the force applied to the football to be equal to the mass of the football multiplied by the acceleration of the foot that kicks the ball. This means that the greater the acceleration of the foot the greater the speed of the ball.
Newton’s 3rd Law states that every force has an equal and opposite reaction force. (Blazevich, A., 2012). The equal and opposite forces that enact when the football is kicked is the friction that occurs between the ball and the foot when contact is made. Gravity forces the kicks flight path to reach a certain height depending on angle and speed of release and then start to descend towards ground and in the direction of the intended target (If skill is executed correctly).
Run up:
The run up stage is vital for the subject to balance, gather momentum, produce horizontal velocity and position their body appropriately to successfully execute the skill (Blazevich, A., 2012). Executing a drop punt is much more difficult from a standing start than a running start due to balance and shifting of weight playing a major role in the drop punt.
Planting of the support Leg:
Plantation of the support leg is vital in order for participants to complete a successful drop punt. The support leg shifts weight to one side of the body to allow an appropriate leg swing by allowing the body to brace and also providing balance and correct positioning of the hip allowing participant to kick football in desired direction (ball, 2013).
(Figure 2. Planting of support leg (last stage of run up motion))
Ball Drop:
To execute a drop punt effectively, the ball must be guided down with the hand cradling the ball and with the release point being at the time the kicking foot leaves the ground, thereby giving the player time to generate power to kick the ball (AFL community). The ball is released from hip level having had the guiding hand controlling the path and orientation of the ball.
During this process the non-guiding hand comes off the front of the ball and swings up horizontally from participants shoulder to provide stability and balance (AFL community). It is important to ensure the ball is vertical at the time contact is made with the foot, which will allow the player to kick the bottom third of the ball, causing the ball to spin backwards and in turn leading to a more accurate kick (AFL community).
(Figure 3. Correct ball drop technique, note ball is almost vertical to allow for accurate foot – ball contact)
Leg Swing:
During the forward leg swing, the ankle is plantar flexed and both the foot and knee extend in sequential summation (Millar, 2004). Foot – ball contact occurs when the knee is positioned at between 30 and 50 degrees of flexion (Millar, 2004). When contact is made with the ball, to improve accuracy toes should point towards intended target allowing for correct contact and greater accuracy (AFL Development, 2013).
(Figure 4. Movements of leg swing in performing AFL drop punt)
Contact:
Contact is seen as the most critical point or stage of kicking these days by AFL kicking coaches and experts (AFL Development, 2013). An important aspect for a participant to make correct contact with the ball is the instep. The instep is when the ankle is fully extended, this allows for the contact to occur on a stable and firm surface which allows for solid contact (AFL Development, 2013). Instep is important for players to correctly execute the drop punt as it gives the ball a solid surface to react with (AFL Development, 2013). This reaction between the accelerating foot and lower leg and the downward moving football (from hand to foot) moves the ball in the direction the toe is pointing to. As Newtons 3rd law states; each action has an equal and opposite reaction, the action is the football moving towards the intended target and the reaction is the friction between the ball and foot and the pressure felt by the foot on contact (Blazevich, A., 2012).
Levers:
When kicking an AFL football the kicking leg acts as a third-class lever (University of Waikato, 2007). The axis point of leg is at the knee and the force moves in the direction from the backside of the body towards the front, this means that the resistance acts in the opposite direction. The longer the lower leg is (distance between the knee joint and the foot) the greater the distance between the axis point and point of contact. The longer this distance is, the greater the angular velocity is and therefore the more power or velocity that can be produced over the same period of time (University of Waikato, 2007). These factors show that participants with longer lower legs should be able to execute a more powerful kick than those with a shorter lower leg, however this isn’t the case. As timing, flexibility and muscle strength can also affect maximum power (University of Waikato, 2007).
(Figure 5. Kicking action in reference to kicking leg acting as a 3rd class lever)
Ideal Trajectory:
When working with projectile motion there is a number of areas that need to be taken into consideration, some of these can be altered by the performer, however some factors are inevitable and uncontrollable (Blazevich, A., 2012). Wind is one factor that can’t be controlled by performers and some techniques may require altering to allow for a change in the footballs flight path due to the direction and strength of wind. For the purpose of this blog, wind speed will remain neutral in order to discuss ideal trajectory in the perfect environment.
The angle of release and release speed are important components of projectile motion (Blazevich, A., 2012). As we are trying to reduce the time it takes to get from the foot to the target the kicker must aim for a high release speed (the perfect speed is mentioned in part 3) and reduce the release angle. (Cook & Strike, 2000) The perfect release angle will change for each person. Autonomous elite footballers are able to kick the ball at a high speed and at a low angle which allows for minimal air time for the ball to reach the intended target. Associative club footballers are not going to be able to produce as much power and kick the ball at the same angle as it may not reach the intended target due to lack of power.
Another area that is of concern with projectile motion is height of release (Blazevich, A., 2012). When kicking the football, the height of release is the point that the ball leaves the foot after initial contact is made. These results conclude that a low release angle and high release speed is the most effective method in kicking a drop punt. However, this is a hard skill to master and is usually only perfectly executed by elite performers.
Follow through:
A drop punt requires a follow through motion to continue to develop power throughout the complete kicking motion and also providing the performer with forward momentum to allow for running stride to continue. Following through with kicking motion also allows for higher accuracy as the kicker can point their foot towards intended target and reduces risk of missing intended target.
(Figure 6. Completing follow through of kick and completing skill)
Below is a link to a complete drop punt performed by Nathan Buckley, an elite level AFL footballer.
How else can we use this information?
This information may be useful for coaches at any level when either first teaching a participant to kick a drop punt or trying to perfect an elite performers kick. Physical education teachers may be able to use some of this information for any Australian rules units they may have to teach. Coaches and teachers level of depth for use of this information will be dependent upon both time frames with the number of lessons a teacher may have or the time at training a coach may have, also the skill levels of participants will greatly effect the level of depth that teachers and coaches may go into and the level of information provided that will be used.
References
AFL Development. (2013). Basic Mechanics of Kicking. Retrieved April 22, 2012, from http://www.aflcommunityclub.com.au/index.php?id=424
Arend, S. (1981) Developing the substrates of skilful movement. Motor Skills: Theory into Practice, 4(1), 1–10
Baker, J. and Ball, K. (1993) Technique considerations of the drop punt. Unpublished. Australian Institute of Sport, Belconnen
Blazevich, A. (2012) Sports Biomechanics: Newtons Laws, A&C Black Publishers, Bloomsbury, London, p 43-50
Bober, T., Putnam, C. A. and Woodworth, G. (1987) Factors influencing the angular velocity of a human limb segment. Journal of Biomechanics, 20, 511 – 521.
Chew-Bullock, T. S., Anderson, D. I., Hamel, K. A., Gorelick, M. L., Wallace, S. A., & Sidaway, B. (2012). Kicking performance in relation to balance ability over the support leg . Human Movement Science, 31(6), 1615-1623.
Huang, T. C., Roberts, E. M. and Youm, Y. (1982) Biomechanics of kicking. In: Ghista, D. N. (Ed), Human Body Dynamics. Clarendon Press, Oxford, 409 – 443.
Knudson, D. (2007). Fundamentals of Biomechanics. USA. Springer.
Orchard. J., Walt, S., McIntosh, A. and Garlick, D. (1999) Muscle activity during the drop punt kick. Journal of Sports Science, 17 (10), 837 – 838
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.
Media
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Video – https://www.youtube.com/watch?v=aj1fGrHTls8
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