Biomechanics in American Football | The Quarterback Throw

Introduction to American Football

American football has origins within England through the 19^th century, where a soccer player decided he was sick of be constrained to only using his feet in the game, he then proceeded to pick up the ball and run it down the field. Obviously this was against the rules in soccer, but this made way to the development in the game of rugby (Embassy, US. 2010). This new sport become a worldwide success and reached America during the 1800’s, it was mainly popular in north-eastern colleges, but then found it’s way across the countries other main universities. Over time the round ball changed form to an 'egg shape', at this time the game of football was very different to the game played now. During the 1800’s rules were changed and manipulated until a final verdict was reached. In 1920 there were more than 10 professional football teams across the United States, and in just over 10 years later, the first National Football League (NFL) championship game was played (Embassy, US.2010). 

The position of the ‘quarterback’ is derived from the positions in the game of rugby, where positions of half and full back existed. This is where NFL manipulated the rules of their game to allow for a forward pass, which the quarterback is responsible. The quarterback has one of, if not the most important job within the team and game of NFL. The quarter back receives the ball, and in a split decision must make an accurate pass to another receiving player. The quarterback must absorb a number of changing variables, make a decision, and make the pass. With millions of viewers, fans, and economic parties across the globe the quarter back must make their decisions and passes, or risk their multi-million dollar contracts. An example of this is Ben Roethlisberger a quarterback for the Pittsburgh Steelers, he is the eleventh highest paid athlete for 2015, earning $48.9 million a season (Badenhausen, K. et. al. 2015).This illustrates the importance of good technical form within the skill and a technical comprehension of the game play.

What are the optimal biomechanics of the quarterback throw, in American Football?

There are a number of variable factors that can influence the play within the game of NFL from defensive, offensive, or special plays. The coaches offensive play tactic will influence what the quarterback is to do from the ‘snap’ (beginning each play), the quarterback will usually then proceed with a passing or running play. Depending on the defensive play chosen from opposing team will influence the decision of the quarterback in the offensive play. It is important for the quarterback to receive and release the ball as quick as possible so as to not get sacked (tackled before releasing the ball) as this can result in negative yards or a ball turnover, which can alter the overall result of the game. From the snap the quarterback must then analyse the changing conditions on the field and make the pass to one of their receivers in order to gain yards in order to get into the end zone. 

The answer through  the biomechanics

The step and gather 

The step and gather is the first stage of the quarterback throw, this is an important stage of the skill as it provides the quarterback the opportunity to read the play and make a decision on what to do in that moment of the game (Fleisig, G. et. Al. 1996). The quarterback will take a number of steps back away from the line of scrimmage, stopping with a wide footing providing a stable centre of mass (Blazevich, A. J. 2013). The quarterback will hold the ball near the chest, with the leading shoulder facing the direction of play.  This helps to maintain the control of the ball, while maintaining high eyesight over the field of play thus helping gather the information of the play. Image 1, Tim Tebow demonstrates the biomechanical aspects within the step and gather in the quarterback throw. His eyes are looking down the field analysing the field of play (indicated in yellow), his leading shoulder is facing down the field toward the target options (indicated in blue), the ball held close to the chest (indicated in red), ready to deliver the ball to one of his receivers. The position of the body in this stage of the throw allows the player to generate torque (Blazevich, A. J. 2013).

Image 1, Tim Tebow in the step and gather, shoulder and eyes facing down field, with the ball close to the chest (Authorityfootball.com 2015).

The leading arm

The leading arm plays an important role in the quarterbacks throw, it provides angular velocity within the throw (Fleisig, G. et. Al. 1996). The angular velocity of the leading arm is the angle of extension at a specific point in the delivery; in this case it is when the leading elbow is at its highest point before the throw. The greater the angle of the leading arm will influence the angular velocity (Image 2, indicated in orange), and the overall speed of the throwing arm and ball speed (Blazevich, A. J. 2013). This encapsulates Newton’s third law,” for every action, there is an equal and opposite reaction” (Image 2, indicated in yellow and red) as the leading arm is pulled down the throwing arm is pulled up into the cocking position (Blazevich, A. J. 2013). 

Image 2, Tim Tebow ready to throw the ball with the leading arm pushing away from the body, with an equal and opposite reaction of the throwing arm (Authorityfootball.com 2015).

The throwing/cocking arm 

The cocking arm is in direct relation to the leading arm velocity and Newton’s third law of motion, as they are an opposite reaction of one another (Fleisig, G. et. Al. 1996). The key phase of the cocking arm it reach a 90 degree angle from the arm pit to the hand (image 3, indicated in yellow), the forearm and hand should be parallel to the mid-line of the body (image 3, indicated by yellow). This produces torque through angular velocity, where the magnitude of the force produced causing rotation of the body is known as the moment of force (Blazevich, A. J. 2013). Newton’s third law states that “The acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object”, this is directly related to the force produced by the quarterback. Increasing the force production to overcome the inertia can be altered by technical changes. Tucking the arms and ball in close to the body can help generate the power in the earlier stages of the skill, as they are closer to the primary source of power, which in this case is the trunk and shoulders (Blazevich, A. J. 2013).  The throw can utilise linear velocity as well, although it is usually reliant on the angular velocity, as the quarterback doesn’t always get the chance to accelerate along a flat straight line.   The acceleration of the arm is the rate of change in velocity from the cocked position to the ball release; the acceleration is a vital aspect of the throw as it indicates how fast the ball will leave the hand (Blazevich, A. J. 2013). The faster the ball is travelling through the air, in theory means it should arrive at the target faster and is less likely to be intercepted by an opponent. 

Image 3, Tim Tebow ready to throw the ball with the throwing arm cocked at 90 degrees, parallel to the mid-line of body (Authorityfootball.com 2015).

Follow through 

The throwing follow through is derived from momentum, as the force generated through the throw is transferred into the ball, the throwing arm will hold the momentum and follow through after the ball is released (image 4, indicated in orange). The greater the force produced in the throwing movement, the greater the momentum followed through from the throw. The plant foot is a key component in reducing and stopping this carry through momentum, this is called braking impulse (Blazevich, A. J. 2013). This is when the plant foot is placed in front of the body’s centre of mass, and it relates directly to Newton’s third rule. As there is a large force placed on the foot as it hits the ground (image 4, indicated in yellow), there is an equal and opposite reaction force (which is also called the ground reaction force GRF) which is transferred back toward the body (image 4, indicated in red) and thus lowering forward momentum and propulsion of the body (Blazevich, A. J. 2013). 

Image 4, Tim Tebow ready to throw the ball with the plant foot ready to stop momentum of the body after the throw (Authorityfootball.com 2015).

Projectile motion

Projectile motion refers to an object (in this case a ball) projected at an angle into the air. Gravity and air resistance are considered to be the main aspects that affect the projectile once in the air. The flight path of the ball is dependent on the trajectory of the ball, this is the angle and speed of release of the ball (Blazevich, A. J. 2013). The range of the ball is directly affected by the projection speed. In theory, the faster the projection speed, the further the ball will go. The angle of projection will greatly affect the trajectory of the ball also, generally 45 degrees is considered optimal, but in the case of NFL, the angle may differentiate each throw depending on the offensive set play. This is where the relative height of projection becomes a defining factor taken into consideration for the quarterback. The relative height of projection refers to the vertical point of release compared to where it lands. If the ball lands (or caught) at a higher point then release, this is classified as positive. Whereas is the ball lands below the point of release, this is negative (refer to image 5). This can make the projection angle a defining aspect when considering accuracy of the throw, depending on where the ball is to land, or be caught will alter the trajectory angle (Blazevich, A. J. 2013). 

Image 4, Shows the difference in positive and negative relative release height, with reference to release angle (Blazevich, A. 2013).

Fluid Dynamics - Drag

Projectile motion of the ball is directly related to fluid dynamics, this refers to the resistance on the ball whilst in flight. When the ball is projected into the air it will experience drag force, this is where particles in the air contact the ball and reduce the amount of kinetic energy of the ball (Blazevich, A. J. 2013). This reduction of kinetic energy will consequently reduce the amount of velocity the ball has while in flight. One way to reduce the drag on an object is to minimise the area, this is where the design of the American football is different to most other sports. By shaping the ball with long leading edges increases the angle that particles will come in contact with the surface of the ball, this allows the ball to cut through particles easier than that of a larger/flatter surface would, refer to image 5 (Blazevich, A. J. 2013). The shape on the other side of the object is also important when referring to drag. If there is a flat surface behind the object this will create turbulent flow, this is due to particles moving from high pressure to low pressure filling the space behind the object, this also reduces energy of the object, refer to image 6 (Blazevich, A. J. 2013). If the object has a long leading edge at the rear also, this will allow particles to move around the object producing laminar flow (Blazevich, A. J. 2013). The spin the quarterback puts on the ball is also important, as this allows the ball to remain on a steady axis, thus reducing the effects of drag and allowing for better aerodynamic performance (Blazevich, A. J. 2013). This is an important aspect in the throw as it allows for better accuracy and speed of the ball while in flight.

Image 5, Shows the difference of particle flow around different shape objects indicating that the object with longer leading edges, separates the particles a lot better (Blazevich, A. 2013).

Image 6, Shows the difference between laminar and turbulent flow depending on the shape of the object's backside (Blazevich, A. 2013).

How else can we use this information?

There are a number of biomechanical aspects mentioned within the blog, these aspects can be implemented into training programs to help develop an understanding of the optimal biomechanics of the quarterback throw (Wuest, D. et. al. 2009). The skill can be broken down into small sections to allow the player to develop their understanding of what they can do to manipulate and refine their ability in performing the skill (Davids, K. et.al. 2008). These biomechanical aspects can be applied in a number of other sports, as they are a base of knowledge to help refine and understand the way the body works when performing select skills (Wuest, D. et. al. 2009). The biomechanics can allow coaches, teachers, and players the ability to understand how to improve results through the complex systems theory (Davids, K. et.al. 2008). This is the process of integrating a number of complex systems and movements to understand and increase skill level.

References

Authorityfootball.com,. (2015). The Quarterback Mechanic: 4 Keys to Optimal Throwing Motion | Authority Football. Retrieved 16 June 2015, from http://www.authorityfootball.com/x-and-o-labs-and-the-quarterback-mechanics

Badenhausen, K., Lawrence, M., Estevez, D., & Wood, R. et al. (2015). Ben Roethlisberger. Forbes. Retrieved 18 June 2015, from http://www.forbes.com/profile/ben-roethlisberger/?list=athletes

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

Davids, K. W., Button, C., & Bennett, S. J. (2008). Dynamics of skill acquisition: A constraints-led approach: Human Kinetics.

Embassy, U. S. (2010). History of American Football.

Fleisig, G., Barrentine, S., Escamilla, R., & Andrews, J. (1996). Biomechanics of Overhand Throwing with Implications for Injuries. Sports Medicine, 21(6), 421-437. doi:10.2165/00007256-199621060-00004

Wuest, D. A., & Fisette, J. L. (2009). Foundations of physical education, exercise science, and sport. McGraw-Hill Higher Education.