Stage 1: Tactical awareness.
Optimal performance across all areas of netball requires tactical awareness, with many studies used within Grobbelaar and Eloff’s (2011) study, proving the high importance of this psychological skill. As seen in the picture above there are fourteen people on the court, seven per side. With only one ball in play there are many movements occurring off the ball. Hooper (2003, cited in Pill, 2014) explains performance of a game in a continuous cycle of reading the play, responding, reacting and recovering; to begin the cycle again. As seen below in the diagram, tactical awareness drives performance.
The aim of an intercept is to gain possession of the ball from the attacking team. This is done by tactile movement and reading play resulting in the defensive player becoming between the two attacking players throwing the ball, jumping to gain air to receive the ball without touching the other players (O'Donoghue, Mayes, Edwards, & Garland, 2008). The player must be aware of their opponent’s movements off the ball, as well as the players around them. Blazevich (2014), describes mechanical energy in two forms, potential energy and kinetic energy. Mechanical energy is a vital biomechanical principle in this stage, as the player needs to have the potential energy to become aerial as the ball approach's and/or the kinetic energy to run with their player who may make a lead towards the ball. Potential energy is described as holding position whilst having the potential to move; once it moves the energy is then kinetic energy (Blazevich, 2014). Potential energy is seen in the player as they position themselves in a manner whereby they are able to view the different players and predict (read play) where the ball is going, while analysing the speed and height of the ball movement. This prepares the player to have more kinetic energy as the ball movement progresses and moves into their line of play or surrounds.
Stage 2: Footwork and arm movement.
Progression from potential energy to kinetic energy is applied during this stage. As the player is aware of their surroundings and ball movement and play is coming into their direction movement from the attacker and defender will become more pronounced. The video above shows the transition from potential to kinetic energy. To ensure the defender is able to perform this skill within the rules of netball, by making no contact with their attacking opponent (Pill, 2014), the player must be on their toes with the potential to move; whilst ensuring their arms are not holding or touching the opposition. Any contact made by a player is a violation of the rules and a penalty is granted for the opposing team (Pill, 2014), below is a video showing contact on the defender trying to hold front position.
The player at this stage is on their toes as a means to increase momentum that will be required to move, which may at the time be to an unknown position. The impulse-momentum relationship is coming into play, as the player is preparing to accelerate themselves towards the ball (Blazevich, 2014). As play comes closer to the defensive player, more movement will occur, showing an increase in impulse within their movements; such as bouncing side to side and/or faster feet movement up on their toes. This allows the impulse to build up, therefore; allowing the player to change their inertia to exert a stronger momentum when action is required (Blazevich, 2014).
Stage 3: Agility- Run-up/approach.
Once the ball is within close proximity to the defender and their attacker, the momentum of both players increases. At this moment velocity is applied by both players. As the defender is aiming to intercept the ball without giving away a penalty, it is essential they are able to successfully create the momentum built up in stage 2 and be agile to respond to the direction of play happening in front of them and the direction of their player. "Agility has been identified to be inclusive of rapid, movements involving the whole body in which changes in direction and/or velocity occur in response to a stimulus" (Hewit, et al., 2012. p.493). As the defender begins their approach towards the ball movement, the player’s centre of gravity (mass) will begin inside their base of support. As the player begins to accelerate, their body will lean forward outside of their base of support, this will cause a forward rotation of their body (Blazevich, 2014). Acceleration (a) is “the rate of change of velocity” (Blazevich, 2014, p. 7). The greater the forward lean, the greater the acceleration (Gaudet, 2014). Gravity plays a role in acceleration, as it can also provide a force when “leaning forward towards the direction of acceleration (or away from the direction of deceleration when we stop) [this] can help us move faster with less muscle force” (Blazevich, 2014, p. 67). As force is applied by the defender on a horizontal and vertical level to move forward, as they jump, their stride differs to help propel them through the air, straightening up their body from the acceleration lead; swinging there legs forward as the impulse momentum is applied to the body in the air. The video below shows the run-up in slow motion, with the landing incorporated.
As the defender is changing their state of motion, Newtons second law is enacted as they are required to apply a stronger force to accelerate and/or change direction quickly. The lighter (mass)the player the faster they will accelerate, as less force is needed to cause the required acceleration (Blazevich, 2014). Whilst running, the defender is thus engaging in Newtons third law, as the stride of the foot hits the ground, a ground reaction force (GRF) is applied to the foot as a reaction to the force applied when the foot strikes the ground. This reaction allows the person to continue running, without sinking into the ground. As previously built up in previous stages the defender is now able to apply the required force required to change their inertia (Blazevich, 2014).
"Notice the arrows indicate the magnitude (length of arrow) and direction (direction of the arrow) of the force vectors" (Blazevich, 2014, p. 45).
Stage 4: Take
off/ jump.
As previously mentioned in stage 3, as for running, GFR is an important element when jumping. “The success of either a vertical or horizontal jump is determined by velocity at take-off” (Ruddock, & Winter, 2016. p. 584). The force applied by the player with the foot on the ground at a slight horizontal and vertical position will have an opposite reaction with the earth (ground) apply force back to the player to jump up. To execute a timed jump, the play has to encompass all three of Newtons laws; applying force to change their inertia and applying force to the ground with their feet creating an equal and opposite reaction with the earth (Blazevich, 2014). The variance of the jump and/or leap required to intercept the ball will be determined by the player for what is going to be the best height and distance required to obtain the intercept. As the player prepares to jump, their arms will swing to, creating other parts of the body to rotate, thus angular momentum will shift; although momentum moving forward will continue. The jump is timed by precision, which is gained by information the player has picked up by watching play and establishing tactical awareness, impulse-momentum and reacting to a force to change their inertia (Blazevich, 2014). As the player has already engaged in impulse-momentum relationship, started in stage 2, the players mass is "moving at an angular velocity, so it has angular momentum" (Blazevich, 2014. p. 78), with a shift in the centre of mass, thus incorporating torque. As a defensive jump for an intercept involves precision of time of force applied, direction and depth; jumping is considered as a vector quantity as both magnitude and direction are key elements for a successful interceptive jump (Blazevich, 2014; Ruddock & Winter, 2016).
Below is a sequence of 4 photos to breakdown the take off and jump stage.
Stage 1 Stage 2
Stage 4 Stage 3
Stage 5: Ball contact/ landing.
Once the defensive player has utilised the built-up momentum and impulse
created through the previous stages, and executed the force and angular
momentum required to become aerial; the final stage is contact with the ball
and successful landing. As with Newtons first law, the player will
continue until an external force changes the current inertia (Blazevich, 2014);
such as making contact with the ball and landing on the ground. When coming into
contact with the ball, the player can be struck with different types of action
put on the ball by the player who released the ball. A main action of the ball,
which can impact successful contact is known as the Magnus effect on the ball.
The Magnus effect on the ball describes spin put on the ball. As the player who
release's the ball applies spin on the ball, making a pressure differential of
the ball. This can be seen when the ball takes a slight deviated route to what
was initially expected (Blazevich, 2014). Dependent on the efficiency of the
defensive pressure and their ability of torque whilst in the air. Torque can
differ between athletes and their experience to rotate and shit their mass.
Absorbing the impact of landing post the jump, it is important the player lands
in a position incorporating flexion at the hip and knees, while rotating the
torso towards the supported landing position of the rotated body (Dempsey, Elliott, Munro, Steele, & Lloyd,
2012). As the player lands, the kinetic energy built up from the force applied
to jump is distributed through the body and through the absorbed through the
ground. (Blazevich, 2014). Due to the rules of netball, the player with the
ball can only take one extra step on one leg once they land with the ball. This
makes it essential as the defensive player who has built-up impulse momentum and
applied force to jump and intercept the pass, are able to decelerate safely. As
the player lands, their centre of mass is once again shifted as they absorb the
landing, decreasing velocity (Blazevich, 2014). The pictures below shows two different scenarios in which a defensive intercept is achieved at different stages and positions of the game. Both pictures show great front position and elevation from the defender's as they make contact during an intercept, with picture two showing rotation of the body in the air, as the ball was released with a Magus effect on the ball.
