Australian Rules Football: Drop Punt & Torpedo Kick  

Prepared by Jenny Wei & Ashleigh Dyer 

THE QUESTION

What are the biomechanical principles that can increase distance in Australian Rules Football?

CONCEPTUALISING THE ANSWER

Introduction:

Australian Rules Football (AFL) is one of Australia’s most participated and spectated sports, recognized for its fast action plays (Gray & Jenkins, 2010; Orchard, Walt, McIntosh & Garlick, 1998). Elite players within AFL often attain strong mental, physical characteristics which can then correlate with a sound technical and tactical ability (Ball, 2008). The main objective of AFL is to maintain possession, enter the opposition’s defensive space and score either a goal or point, which is therefore, considered an invasion game (Pill, 2013). Players require certain skills including successful disposals, kicking for distance and kicking for accuracy. Gray and Jenkins (2010) state that a long distance shot allows players to have a shot at goals from a longer distance making the kick more difficult for the opposition to defend.

Biomechanical Concepts and Major question:

This blog serves to analyse the skill of kicking for distance in particular by looking at the two kinds of AFL kicks, the drop punt and the torpedo. This blog will compare the two kicks by exploring relevant biomechanical principles. This blog will consider the question “What are the biomechanical principles that can increase kicking distance in Australian Rules Football?"

The following biomechanical principles will be used to address this question;

Ø  Angular Velocity and torque

Ø  Projectile motion

Ø  Impulse- momentum relationship

Ø  Work, power and kinetic energy

Ø  Magnus effect

Ø  Newton’s First law (law of Inertia)

Overview of kicking:

The drop punt kick is the style of kick that is predominantly used within the sport of AFL because of its speed of execution, accuracy and longest distance produced, therefore it is a focus of this blog (Orchard, Walt, McIntosh & Garlick, 1998). However, the torpedo is often used for distance as the spinning of the ball can get it further (Orchard, Walt, McIntosh & Garlick, 1998). Blazevich (2007) states that the AFL kicking action can be described as a ‘throw like’ action where the muscles around the area of the hip accelerate the upper leg before the leg and foot swing through after. The main objective when kicking the AFL football is to generate the highest velocity when contacting the ball to create a longer distance and speed on the ball (Young et al, 2011).

Skill Break Down: Drop Punt

The drop punt offers players more accuracy when comparing to the torpedo, and when considering the aim of the game, it is important for players to keep possession of the ball (AFL Community, 2017; Gray & Jenkins, 2010). As previously stated, the drop punt is the most used style of kicking as it  is more accurate and easier for the receiver to mark (Ball, 2008).

The drop punt kick has many different variations as each individual player has their own slightly unique technique, however, there are some ‘non- negotiables’.  This includes when the ball is guided onto the athletes preferred foot, when the release point is where the athlete swings through the leg. This gives the athlete time to generate power to kick the ball, and the ball will spin backwards, end for end. The extension of the lower leg during this kick should have a firm ankle which gives the athlete a firm platform to kick off (AFL Community, 2017).

(Google Images, 2017)

Skill Break down: Torpedo

The torpedo is quite a different kicking style in comparison to the traditional drop punt. When an athlete kicks a torpedo, the ball is angled slightly away from the body with the end of the ball which is furthest away, pointing down (AFL Community, 2017). Players must make sure when they are in the preparation phase of this kick, that their grip on the ball and guiding angle stays the same, creating a rotation on a long axis of the ball which creates less drag whilst in the air (AFL Community, 2017). This style of kick allows the ball to travel further in the air than the drop punt kick if the force and trajectory were the same.

When discussing the kicking sequence of AFL, there are many different biomechanical principles that can be addressed.

The preparation Phase

Kinetic Energy

Work, power and kinetic energy are all biomechanical considerations that come into play when looking at both the drop punt and the torpedo kick in AFL, particularly in the preparation phase of the kick. The player uses their preferred kicking leg to swing through, extending the knee slightly in order to generate sufficient power (AFL Community, 2012). This extension of the leg will help the player have a firm foot and firm ankle, creating a solid base for the kick (AFL Community, 2012).

During the preparation phase of kicking, the kinetic energy produced can assist the player in maximising their kicking distance. Kinetic energy is the form of energy that is associated with the velocity of our body and can be measured and the motion of movement in one’s body and the complex patterns of these is known as the kinetic chain of energy (Blazevich, 2007). Blazevich (2007) describes the kinetic chain as the characteristics of push-like and throw-like movement patterns. The energy for the kick is

generated in the stage of the kicking mechanics called the limb-loading phase, where the player draws their leg backwards in a rapid motion before swinging it forwards. The drop punt and torpedo comes into consideration as a throw-like movement pattern due to the muscles around the hip that accelerate before the foot swings through (Blazevich, 2007). This throw-like movement pattern allows the body joints to extend sequentially in order to perform an accurate kick with appropriate distance. As we know, the joints of the body extend sequentially, one after the other, whereby in the case of the kick the thigh accelerates before the lower part of the leg, resulting in a higher end point of velocity in the follow through (Blazevich, 2007). Techniques like this require a significant amount of strength and stability from the hip and smaller muscles surrounding the hip joint as well as the gluteal muscles.

Ball Drop

When looking at the drop-punt ball drop, the non-preferred hand plays a significant role in the kinetic energy created and therefore the overall distance of the kick. Players should hold the ball with fingers spread across the seams on the football, removing their non-preferred hand for the purposes of balance. When the non-dominant hand departs the football, a minor rotation coming through from the hips and shoulders to occur. The rotation of the upper body subsequently causes a larger mass behind the ball and therefore theoretically should have a greater kinetic energy output due to the greater mass (Blazevich, 2007). The non-dominant hand also becomes as a counteract to the leg swing during the kick, allowing the player to balance their center of mass, helping to keep their body evenly distributed (Blazevich, 2007).

The hand plays an integral part football drop; however the most critical component is the drop of the football onto the foot. When looking at dominant kicking leg and preferred hands used, if a player kicks with their right foot, the right hand will become the dominant guiding hand and vice versa for the left. The ball will be guided by the dominant hand and dropped at about hip height, vertically over the kicking leg, allowing the player to make connection to the lower third of the ball creating a backwards spin (AFL Community, 2012). This would be considered an effective drop punt as the backspin allows the football to achieve a greater range due to the Magnus Effect which is explained in more detail in this blog. When the athlete drops the football, the torso will shift from a position leaning more forward, to a slight lean backwards, as shown in figure 3 below (Blazevich, 2007). This positioning of the trunk is most ideal as it allows more time and space between the guiding of the ball to the ball drop, allowing for greater accuracy, longer contact time and more control over the ball (Blazevich, 2007). Other factors that are essential for accuracy must also be taken into consideration. The player must ensure that the angular velocity is constant from the run up as any deviation could cause for an inaccurate kick.

(Google Images, 2017)

Leg Swing

Angular Velocity

The concept to be discussed when talking about the leg swing component of the kick is the idea of angular velocity which is simply the rate of change in the angle of the leg, where the fast the leg swings through, the quicker the ball will move. A study undertaken by Ball (2008) found that the angular velocity found with shorter distance kickers was 1405°/s compared to 1554°/s with the longer kickers. Using the equation;

“ The equation of a circle is 2p radians= 360° ,therefore π radians =180°. Knowing this information allows us to convert degrees to radians: radians = degrees/(180/π) or degrees/57.3." (Flinders, 2017).

Angular Velocity (ω) = Δθ/Δt

Therefore, 1405/57.3= 24.5 Radians (rad.s) and 1554/57.3=27.1 Radians.(rad.s)

=24.5 rad.s x leg length of 0.85m

= 27.1 rad.s x leg length 0.85m

Therefore, 24.5 x 0.85= 20.9 m.s-1  and 27.1 x 0.85= 23.03 m.s-1

It can be seen that there is a difference between a shorter kicker and a longer kicker when comparing lower leg angular velocity with a difference of 2.13m.s-1. According to Blazevich (2007),AFL players that have longer legs have a greater release velocity which indicates that leg length is important  to AFL forwards. To increase the kicking range in football, it is exressed by Ball (2008), is to increase lower leg angular velocity at the contact point. This is where torque becomes a biomechanical consideration. When the player swings their lower leg and foot through to kick, the muscles which surround the hip such as the gluteus maximus and the hamstrings produce force away from the hip which is known as torque (Blazevich, 2007). This torque production can produce a higher angular velocity for the athlete which can increase the distance of the kick. Some of the skills and drills Ball (2008) found that could help increase distance is increasing the last step, however, the step needs to be proportional to the run up speed, as over-striding can inhibit the player’s kick (Ball, 2008). The player could also attempt to kick the ball higher off the ground and further away from the body when contacting the ball. Although angular velocity has been found to manipulate the distance of the kick, there are also ball flight considerations and characteristics that could also alter these results. These are things such as different angles of trajectory (projectile motion and projectile angle), spin of the ball and the rate of the spin of the ball that will now be discussed in further detail.

(Google Images, 2017)

Ball Contact with the Foot

Projectile Motion:

As angular velocity has been discussed, the contact of the foot needs to be explored where the projectile motion component comes into effect. Blazevich (2007) and Watts and Moore (2003) state that projectile motion is the motion  in which the football is released into the air. As the footballs trajectory is influenced by the projection speed, projectile motion is considered an important part of the AFL Kick when going for the maximum distance (Blazevich, 2007).The  range in which the football takes is the result of the ball's horizontal velocity and the time in the air.

Range=  (Vh.t)

The diagram above shows the different  projection angles that the football can be released after making contact with the ball, to achieve maximum distance. The diagram can be explained as the higher the ball is projected off the foot, the less horizontal range it will have. The diagram indicates that the optimum projection angle for the football is 45 degrees as the ball will have the equal magnitude of it horizontal and vertical velocity, and the ball’s range can be gained (Blazevich, 2007). However there needs to be other aspects that need to be taken into consideration such as gravity and air resistance.

(Projectile Motion in the NRL- National Science Foundation, 2015)

Impulse – Momentum Relationship

When wanting to change an object's momentum (the AFL Football in this case),  players apply a greater force to the object, and they can also apply that force for longer. Therefore impulse momentum is the force that is applied onto the footy by the time it has incontact with the player's foot and a greater impulse means that there is a greater change in momentum. Because of the impulse-momentum relationship, the longer the player can have in contact with the ball, the greater the velocity on the ball at the point of impact on the foot, making the ball go a bigger distance (Young et al, 2011).

 The Follow Through

Newtons 1st Law/ Drag

When analysing the biomechanical principles of the torpedo kick, it is crucial to analyse the way in which the ball itself travels, particularly after optimal projection motion occurs. The drop of the ball onto the foot and the contact with the ball itself causes the noteable spiral motion, allowing it to effectively spin through the air (AFL Community, 2012). If this spiral motion is maintained during the flight process, the more stable the ball will be as the airflow surrounding the ball itself will allow for longer time in the air as well as less drag (Watts & Moore, 2003).

When looking at the concept of stability in the more commonly used kick, the drop punt, the ball spins backwards and therefore does not have the same stability the torpedo kick gains through the spiral motion, thus the ball is forced through the air and drag is created, which subsequently reduces the possible distance travelled (Blazevich, 2007).    

With this information, Newton’s first law of motion (law of inertia) which states that “an object will remain at rest or continue in motion unless acted upon by a force” can be applied (Blazevich, 2007). The ball should continue in motion and remain in flight unless acted upon by another force. In the case of the torpedo kick and the drop punt kick; the force acting upon the ball is that of the mass of the ball and the air surrounding it. As aforementioned, the torpedo kick has a reduced drag due to its spiral motion and thus the force of the surrounding air is reduced, allowing for greater time in the air and therefore greater distance.  The drop punt does not utilise this spiral motion, where it's backwards spin does not cut through the air but instead disrupts the airflow around the ball which therefore creates more drag, dropping its trajectory faster than the torpedo quick would (Blazevich, 2007).

Magnus Effect:

By applying Newton’s Third Law, it is evident how the ball reaches the desired location in reference to the amount of force applied from the foot to the contact of the ball from the momentum gained in the kinetic chain (McGinnis, 2013). However, the ‘Magnus Effect’ also comes into play, as the kick must not only reach its target but also account for distance travelled in the air.  In the case of football, the ball is contacted upon underneath at a particular point that allows the ball to travel in the air with a backwards spinning motion. The ‘Magnus Effect’ explains that a spinning ball will ‘grab’ the air that flows past it due to the friction between the air and the ball, thus causing the ‘Magunus Effect’ as seen in Figure 4 (Blazevich, 2007). This backwards-spinning motion allows the football to remain in the air for longer with a more accurate trajectory path (Blazevich, 2007). As the ball spins backwards, the air will flow around the ball and act against it, subsequently allowing the ball to stay up in the air for longer. The Magnus Effect has a greater affect on the drop punt kick in a greater capacity in that it creates a more controlled kick, keeping in mind that spin an individual applies to the ball will also have an effect by causing a pressure differential, causing the ball to start to swerve (Magnus effect). To limit the Magnus effect, a kicking technique that focuses on accuracy and distance is optimal, as to promote backspin and avoid missing the target. It is evident that the Magnus Effect affects the drop punt kick in a larger capacity than it does the torpedo, as it causes the drop punt to be a more controlled kick (Blazevich, 2007).

(Google Images,2017)

The Answer

When an athlete is kicking for distance, the information discussed above indicates that the torpedo can achieve this in comparison to the drop punt. For the athlete to generate a greater angular velocity of the lower leg creates a greater foot speed when the foot makes contact with the ball. If the ball is projected with greater motion and a projection angle of 45 degrees, the ball has a greater opportunity to achieve a greater range. During the balls flight time, the spiral motion of the torpedo has reduced drag in comparision to the drop punt that has a higher amount of drag in the air.

How else can we use this information?  

The information provided in this blog about kicking for distance in AFL can be applied in many others ways across many different avenues such as teachers and coaches. This information could be used for tactical purposes in different contexts such as the final 5 minutes in the fourth quarter of the game or the first 5 minutes of the game when distance is either critical or not. Young et al (2011) indicated that the biomechanical principles that are discussed with AFL kicking can be transferred to other sporting codes such as soccer. Not only could this be used for coaches, teachers in the education sector could use it to allow students to get as much as they can out of lessons and understand how they can increase their kicking distances.

 References:

AFL Community. (2012, August 2). Kicking Guide (for players) – 2. Basic Mechanics of Kicking. [Video File]. Retrieved fromhttps://www.youtube.com/watch?v=gdRfAFBEj-M

AFL Kicking. (2017). Google Images. Retrieved 19 June 2017, from https://images.google.com

Ball, K. (2008). Biomechanical considerations of distance kicking in Australian Rules football. Sports Biomechanics, 7(1), 10-23.

Ball, K. (2008). Foot interaction during kicking in Australian rules football.Science and football VI, 36-40.

Blazevich, A. (2007). Sports Biomechanics: the basics. Optimising human performance. A&C Black.

Gray, M. A. J., & Jenkins, D. G. (2010). Match analysis and the physiological demands of Australian football. Sports medicine, 40(4), 347-360

 McGinnis, P. (2013). Biomechanics of sport and exercise. Human Kinetics.

Orchard, J, Walt, S. McIntosh, A. & Garlick, D. (1998). Muscle Activity during the drop punt kick. SportHealth. 19-24.

Pill, S. (Ed.), (2013). Play with Purpose 3rd Edition: Game Sense to Sport Literacy. Hyde Park Press. Australian Council for Health, Physical Education and Recreation (ACHPER)

Watts, R. G., & Moore, G. (2003). The drag force on an American football.American Journal of Physics, 71(8), 791-793.

Young, W., Clothier, P., Otago, L., Bruce, L., & Liddell, D. (2004). Acute effects of static stretching on hip flexor and quadriceps flexibility, range of motion and foot speed in kicking a football. Journal of Science and Medicine in Sport, 7(1), 23-31.