What factors determine a successful free throw in basketball?

What is a free throw?

In Basketball, free throws (also known as foul shots) are unopposed attempts to score points from a restricted area on the court (the free throw line). Free throws are awarded for a number of reasons during a game including: when a team commits a set number of fouls in a set period (whether or not in the act of shooting), a technical foul, an unsportsmanlike foul, and the most common, after a foul on the shooter by the opposing team. As there is no time limit and no one defending the shot, the free throw is a ‘closed skill’; it is also considered a basic shot for basketball players (Uchida, Mizuguchi, Honda, & Kanosue, 2013). The shot is taken from the foul line, 4.6m from the ring and each successful attempt is worth one point.

Free throws have the potential to impact the outcome of a game and are said to be the deciding factor in winning or losing a game (Kozar, Vaughn, Lord, Whitfield, & Dye, 1994). The scores gained from free throws typically count for more than 20 per cent of the total score (Krause & Hayes, 1994); thus highlighting the importance of an accurate and therefore successful shot. Successful free throw shooting requires good concentration, but most importantly good mechanics in the shot.

In order to answer our question, we take a closer look at the biomechanical skill cues in each of the four movement phases and consider the biomechanical principles that influence the success of the skill. 

  

Breakdown of Movement Phases

1. Preparation phase:

• Stance – balanced, with hips square to the hoop. Feet can be staggered or directly on the line. The feet are placed close to shoulder width apart for the shot, or slightly wider apart, depending on player preference. Foot placement too close together may produce balance problems for the shooter, as the base of support is then very narrow, while foot placement too wide apart will introduce a lateral component to the push of the feet on the floor.
• Bend knees. Stretching your hamstrings will allow a deeper bend at the knees and a more fluid shot. There needs to be adequate power coming from legs as it determines the distance that the ball will travel. If the shot is short = not enough power; if shot is long = too much power.
• Elbow position – bent and tucked in. Gives a more direct angle towards the hoop.
• Shooting hand is aligned with the lines on the ball. This helps with rotation of the ball.
• Non-shooting/ guide hand to the side of the ball, shooting hand facing the basket.
• Focus on target/ just above the ring

The trunk flexion at this stage of the shot is very important, as the subsequent trunk extension is used for loading the legs by increasing knee and hip flexion just prior to the extension for the shot.

Here is where we can apply Newton’s Third Law: ‘For every action, there is an equal and opposite reaction’ (Blazevich, 2010, p. 45). This is relevant in the free throw when a vertical or downward force is applied as the foot contacts the ground. The ground exerts an equal and opposite reaction force which enables the player to accelerate forward or vertical (if the force is great enough to overcome inertia). Figure 1 demonstrates Newton's Third Law. A vertical (downward) force is applied when the foot contacts the ground (A). The ground exerts an equal and opposite reaction force, in this instance called the ground reaction force (GRF), which stops the foot sinking into the Earth.

(Figure 1. Source: Blazevich, 2010, p. 45)

Inertia is relative to the mass of the object. Heavier objects require a larger force to accelerate, which is enlarged when an object is moving vertically due to the gravitational force. This is evident in a free throw as the player is moving vertically, bending their legs and applying force into the ground, to come up on to their toes or to jump slightly. Thus, due to gravitational force players must apply a larger force.

2. Extension phase:

• The sequence of the upper body should be: trunk extension, shoulder flexion, then elbow extension and wrist flexion together.
• Flex wrist and fingers pointing forward, releasing ball off index finger.
• Keep balance on hand until ball is released.

In terms of the kinetic chain, during this phase of the skill we see a push like movement pattern. As the player extends their knee and elbow joints simultaneously in order to generate force, they push the ball in a straight-line movement. 

(Figure 2. Source: Basket ADN, 2014)

Summation of forces

In terms of accuracy, the summation of forces is very important in the free throw. Force summation is the combination of forces produced by different parts of the body. During the free throw, the power for the shot comes from the build-up of energy through all the muscles used in the shot. For example, the legs bend and extend, as does the elbow (causing the whole arm to extend), finishing with a flick of the wrist to transfer the forces into the ball and therefore enabling the ball to make the distance to the net. 

3. Release:

• At release the trunk and legs should be fully extended, and the elbow should be approaching full extension, indicating that these joints have made a full contribution to the flight of the ball.
• The wrist should be in mid flexion at release, a position halfway between full extension and full flexion to ensure that the hand is moving at maximum velocity as the ball is being released.
• Ball rolls off fingertips, not palm.
• The trunk should be rotated away from the shooting hand, to line up the shooting shoulder and arm more directly with the hoop. This trunk rotation is facilitated by the dropping off of the non shooting hand from the ball and helps to propel the ball forward.
• Apply torque for force or spin on the ball that is not linear towards the hoop.

This is also referred to as the Magnus effect that explains how once the ball is released from the player’s hands, the air around it will affect its flight path. A backspin fights against gravity. The more spin, the more the ball will 'hang' in the air. Because the back spin is rotating in the opposite direction that the ball is travelling, the spin causes the ball to slow down and even jump backward once it hits the rim or backboard. In the free throw, the player should apply back spin in order to drag air into the net in a downward force. As a result of Newton’s third law, the air which is forced downward has an equal and opposite reaction/force applied to the ball, pushing it upwards. Therefore a ball with backspin will require less power to make the distance to the net. The following video further explains the Magnus effect.

(YouTube: https://www.youtube.com/watch?v=RRpMek9hmX0)

Wrist flexion provides the final thrust for release of the ball and helps determine both the velocity and angle of projection of the ball (Hess, 1980; Martin, 1981). Here is where we can apply Newton’s Second Law: ‘The acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object F = ma’ (Blazevich, 2010, p.45). In order to shoot a free throw, the player must apply force in order to accelerate the ball.

Studies have reported that shots of highly skilled players are released higher than those of less skilled players; and a higher release is related to greater flexion at the shoulder and elbow extension at release (Hudson, 1982; Yates & Holt, 1983). It is important for the body to remain erect and vertical during the release of the ball. This will ensure optimal vertical velocity is imparted to the ball at release, and will be conducive to a higher release point. In other words, the higher the ball is released, the less time it is in the air before reaching the basket, and the less the release angle decreases. 

Angles of release

Angles of release significantly influence the free throw shot as the chance of the ball going in the ring vary with the angle the ball is released. This angle determines the shape of the ring the ball will fall through. For example, if the ball is falling from directly above, it has the whole diameter of the ring to fall through. As the release angle decreases the shape of the ring becomes smaller, thus the ball cannot fall through cleanly and there is a smaller margin of error. 

(Figure 3. Source: Okazaki & Rodacki, 2012)

This is not to say that shooting with a very high angle of release is best. Players need to consider the strength they are capable of putting into the shot as it takes more effort to shoot the ball the required distance if released at a higher angle than a lower angle, also making it more difficult to control the balls flight path. Angle of release should be around 52 degrees horizontal according to Tran and Silverberg (2008), for a 6 foot 6 player (optimal angle varies with the height of the player).   

Projectile motion

Projectile motion refers to the motion of an object projected at an angle into the air. An objects trajectory can be influenced by gravity, resistance, projection speed, the projection angle, and the relative height of projection. In the Basketball Free Throw, the ball is a projectile. The force exerted upon the basketball is a push, projecting the ball horizontally and vertically; causing the ball to rotate, elevate and swish through the net. The gravitational pull upon the basketball creates the arch; without this pull, the ball would continuously travel horizontally at a constant speed (the law of inertia), this also relates to Newton’s first law. The ball can reach the basket with a high arch or a lower arch, with the higher arch giving the greatest chance for the ball to go into the basket. See figure 4 below.

(Figure 4. Source: McCann, 2014.)

4. Follow through:

• The final phase of the shot is the follow through, in which all the joints continue to move through to the end of their full range of motion following release of the ball. In the skilled follow through, the legs are fully extended and the ankles are plantarflexed (toes pointing to the floor). The trunk is vertical and the shooting hip is lined up vertically with the knee and ankle, as well as with the joints of the shooting arm.
• This movement of the joints to the end point of their range of motion will ensure that the joints do not stop moving prior to release of the ball, which would decrease the release velocity of the ball.
• After the ball has left the hand the elbow should reach full extension, the wrist should be fully flexed, the lower arm should be in pronation and the fingers should be pointing slightly to the outside; indicating that pronation has occurred during the shot.
• Arm stays up until ball goes through net.

Answer

According to Miller (1999), inaccurate free throws were characterised by greater variability in linear speed at segment endpoints than accurate shots; thus a consistent movement pattern is important.

Biomechanically, a full range of elbow movement is related to greater success in the free throw of club level basketball players (Tran & Silverberg, 2008). In mechanically correct shots, the wrist, forearm, upper arm, and right side of the body will be in a straight line and perpendicular to the floor (Ball, 1989).

By breaking down the mechanics of each of the movement phases, we can see there are many factors influencing the success of a free throw shot. According to Tran and Silverberg (2008), of all the parameters of the free throw, maintaining a constant speed is the most important but also the most difficult; as backspin and speed are variables that rely on the shooter’s ability to maintain consistent motion. 

How this can be used elsewhere?

The biomechanics discussed in this blog can be used by coaches and players in Basketball as well as in other sports. The biomechanics behind the angle of release affects many projectiles, i.e. javelin and netball. An understanding of angles of release can be used to determine the optimum trajectory for whatever object you need to throw.

Newton's Laws are important for sporting success in general as they enable athletes and coaches to consider how to optimise force production, and in what direction we should apply these forces. 

The Magnus effect can be applied across a number of other ball sports. By understanding the benefits of spin, performance can be improved. For example, in Rugby, spin is used when passing the ball to improve its aerodynamics; in Tennis spin is used to change the trajectory of the ball; and in Soccer players kick across the ball to put spin on it to curve it around a wall of players at a free kick. Additionally, an understanding of spin is also useful for players not in contact with the ball; for example, in cricket and baseball if the fielder knows what spin was placed on the ball, they will be better able to predict the ball's flight path and which way the ball might spin after it hits the ground.

And an understanding of the kinetic chain is particularly important from a coaching perspective as it helps to determine what type of movement pattern should be adopted according to individual constraints. For example, the same skill may be practiced using either a push or throw-like pattern, depending on whether enough force is produced to accelerate an object (such as a ball). The coach would need to consider the strength and age of the player. This is also related to the summation of forces.

By understanding the biomechanics behind one skill such as the Basketball free throw, we can transfer this to understand the biomechanics of other skills, in the sport of Basketball or other sports that require similar mechanics, as we have highlighted.

References:

Ball, R. (1989). The basketball jump shot: a kinesiological analysis with recommendations for strength and conditioning programs. National Strength and Conditioning Association Journal, 11(5), 4-12. 

Blazevich, A. (2010). Sports biomechanics, the basics: optimising human performance. A&C Black Publishers: London.

Hamilton, G. R., & Reinschmidt, C. (1997). Optimal Trajectory for the basketball free throw. Journal of Sports Sciences, 15(5), 491-504.

Hay, J. G. (1993). The biomechanics of sports techniques (4th ed.). Englewood Cliffs, N. J.: Prentice Hall, Inc.

Hess, C. (1980). Analysis of the jump shot. Athletic Journal, 61(3), 30-32, 37-38, 58.

Hudson, J. L. (1982). A biomechanical analysis by skill level of free throw shooting in basketball. Paper presented at the International Symposium of Biomechanics in Sports, Del Mar, CA.

Kozar, B., Vaughn, R. E., Lord, R. H., Whitfield, K. E., & Dye, B. (1994). Importance of free throws at various stages of basketball games. Perceptual and Motor Skills, 78(1), 243-248.

Krause, J., & Hayes, D. (1994). Score on the throw. In J. Krause (Ed.), Coaching basketball pp. 262–266. Indianapolis, IN: Masters Press.

Martin, T. P. (1981). Movement analysis applied to the basketball jump shot. Physical

Educator, 38(3), 127-133.

McCann, A. T. (2014). Basketball physics: the anatomy of the free throw. Popular Mechanics. Retrieved from http://www.popularmechanics.com/outdoors/sports/physics/basketball-physics-the-anatomy-of-the-free-throw-7556633

Miller, S. (1999). Electromyographic considerations of inaccuracy in basketball

shooting. Paper presented at the International Society of Biomechanics in Sports,

Perth, Western Australia.

Okazaki, V. H. A., & Rodacki, A. L. F. (2012). Increased distance of shooting on basketball jump shot. Journal of Sports Science and Medicine, 11, 231-237.

Tran, C. M., & Silverberg, L. M. (2008). Optimal release conditions for the free throw in men's basketball. Journal of Sports Science, 26(11), 1147-55.

Uchida, Y., Mizuguchi, N., Honda, M, & Kanosue, K. (2013). Prediction of shot success for basketball free throws: visual search strategy. European Journal of Sport Science, 14(5), 426-432.

Yates, C., & Holt, L. E. (1983). The development of multiple linear regression equations to predict accuracy in basketball jump shooting. Paper presented at the Biomechanics in Sports: Proceedings of the International Symposium San Deigo, CA.