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Biomechanics and Skill Analysis

of Scrum-Half Passing Skills Part 1

by

Mark Calverley.

The author is a Pom in New Zealand and he is currently completing the highest

coaching paper (Certificate in Rugby) with the NZRFU and Massey University.

He played for Nuneaton, Warwickshire, Nottingham, Harlequins, England U18, Great

Britain Students and England Students Rugby League. He is now Head of Physical

Education and 1stXV coach at Wanganui Collegiate School in New Zealand.

INTRODUCTION: What is biomechanics? a personal perspective Why use biomechanics? Efficient and appropriate technique.

GUIDING BIOMECHANICAL PRINCIPLES:

Base of Support. Centre of Gravity. Force Summation. Newtons Laws of Motion. Levers. Torque and Rotation. Acceleration distance.

APPLICATION OF THE PRINCIPLES:

HALFBACK SKILLS & PRACTICES

Footwork. Approach. Hand placement (on ball). Rotation (and ball delivery).

IDENTIFYING, ANALYSING AND CORRECTING PROBLEMS:

Video analysis Passing drills and practices


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Centre of Gravity (COG) & Base of Support (BOS).

Standing normally (anatomical position) the centre of gravity (COG) is generallycentrally located in the body at around belly-button height. The COG can be moved in

any direction by moving various body parts i.e. COG goes up if the athlete raises hisarms, goes more to the left if he moves both arms left etc. (Refer Fig 3.)

The base of support determines stability and balance. The wider the base of support

and the more points in contact with the base, the greater the athletes actual

stability.

Notice that the base of support in picture 1 is short and narrow, meaning that he isless stable. He is also less stable because he only has one point of contact with the

ground.

The wheelchair athlete is the most stable as his base of support is wide, spreadover a wider surface area and has four points of contact (wheels). (He also has a

lower centre of gravity.)


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The golfer has two points of contact and a moderate base of support to keep himin balance.

Stability becomes compromised when the Vertical (line of gravity) from the COGmoves towards the edge of the base of support.

Once the GOG moves outside the base of support, the athlete will lose balanceand have to correct his stance or risk falling over.

Example 1 shows the athlete in perfect balance, with his COG directly over theBOS (VLG)

Example 2 shows the athlete in balance, but with the COG moving towards theedges of the BOS (VLG)

Example 3 shows the athlete out of balance as their COG (VLG) is outside hisBOS. He needs to re-set his BOS (or fall over).

The balance of any sportsman may be further improved by lowering the COG (picture1

below) as the VLG has further to travel (i.e. a greater angle,) before shifting outside the

BOS.

For the scrum-half pass, the player will bend his legs slightly in order to add flex to the

swing, but it also to helps to control balance whilst moving and swinging. Obviously a


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COG that was too low would hinder other mechanical principles (i.e. leverage to be

explained later) and needs to be balanced accordingly.


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This picture shows a scrum-half with a wide base of support, a low(ish) centre of gravity

and the vertical line of gravity within the edges of the base of support. The result is a passthat can be executed in balance.

This picture shows the scrum-half with a narrower base of support, a comparatively high

centre of gravity and the vertical line of gravity near the edges of the base of support. The

result is lack of balance and control. The likelihood is that the scrum-half will need to re-adjust his feet andcentre of gravity in order to produce an efficient or effective pass.

Shifting horizontal and vertical positions of the COG through movement.


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Summation of Forces

Successfully completing any passing swing requires that the scrum-halfco-ordinates the

body parts throughout the skill so that they link together, in order, smoothly,effortlessly and in control. This is often referred to as timing.

1. For the forward phase of the pass, the movement and force is initiated in theankles, legs and hips, then through the trunk and shoulders and finally the arms

and wrists finish off the movement as the ball is thrown.

2. Try to complete a number of skills (throwing, hitting and kicking) and work outwhat order the skill forces operate best in. Then try to mix the order up and again

complete the skill. It will feel awkward and success will be limited.


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Obviously, all of the skills need to be linked together at the optimum performance time

for the skill to be successful and with perfect timing. The next graph illustrates two

complete passes. The first example shows the perfect summation of forces, the second

shows the summation in the correct order, but with poor timing.


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Fig 9

Newtons 1stLaw Of Motion

An object at rest (stationary) will remain at rest unless acted upon by an external

force


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Explanation:

This means that the rugby ball will remain stationary until the scrum-half passes it. (Or

some other force affects it i.e. another player, wind etc.)

Newtons 2nd

Law Of Motion

When a force acts upon a mass, the result will be the acceleration of that mass

Explanation:

This builds upon Law 1 to state that when the ball is passed it accelerates. Or, when the

swing is done properly it begins smoothly and ends controlled but fast. Therefore, thearms/body are accelerating towards the desired target.


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For every action there is an equal and opposite reaction

Explanation:

As the scrum-half passes the ball, the opposite reaction is for the ball to accelerate awayproportionately to the force applied to it. ie., a ball passed hard will accelerate quickly,

whereas a ball passed softly will accelerate less quickly.

I have always thought that these Laws of Motion were blindingly obvious and rather

simplistic, but they arenone-the-less true to the principles and techniques we are lookingat.Newtons 3rdlaw( For every action there is an equal and opposite reaction) is themain law in terms of analysing technique, as any problem that occurs at the end of thepass can be traced back to the start of the pass (with the exception of high wind

conditions etc.).

LEVERS

For human movement (including all forms of rotation) there are three possible

levers (called classes 1stclass, 2

ndclass and 3

rdclass) that are used.

There are three parts to each lever:

The LOAD(L)(also sometimes referred to as RESISTANCE) The PIVOT (P)(also sometimes referred to as the FULCRUM) The EFFORT (E)(also sometimes referred to as the FORCE)


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The key part of understanding which level is which (1st, 2

ndor 3

rdclass) is to look at

which part is located in the middle of the lever, as it remains constantwhen the example

is looked at from in front or behind. (Remember also, that the load, effort and pivot canbe shifted to different points on the line this affects leverage potential, leverage

effectiveness, power generated and amount of effort required. These are all points thatyou will experience in your practical application of levers.)

Examples of this would include a Leg Press (below) or Rowing where the oar pivots

around the rowlock. The load/resistance is the water and the rower pulling is the effort.


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For a THIRD CLASS LEVER the EFFORTis always in the middle.

Examples include: Most sporting movements, especially bicep curl, kicking and passing

(see below).

(NB This diagram has been simplified. There are other pivot points i.e. wrists, shoulder

etc. with their own resistance and effort points.)

The 3rdclass lever is the most common in rugby and applies to a multitude of skills(i.e.

kicking, passing, pushing, tackling etc.) The picture above shows the shoulder as the

pivot, the ball as the load and the direction of the swinging arms is the direction of effort.

Once coaches understand how to identify types of levers, the key principle is then to

understand how and why forces are applied and affected by the length of lever.

FORCE ARM V RESISTANCE ARM

The FORCE ARM is the distance from where a FORCE/EFFORT is applied tothe PIVOT


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The RESISTANCE/LOAD ARM is the distance from where aRESISTANCE/LOAD acts in relation to the PIVOT

The length and size of the FORCE ARM and RESISTANCE ARM have a profound and

distinct effect in all sports, and especially passing.

The longer the lever (RA) the greater the swing speed generated. (i.e. long arms produce

greater force and longer passes). However, long levers can be more difficult to control

due to their length.

The shorter the lever (RA) the easier it is to control the ball direction, but less power and

arm speed can be generated (with equal effort) than for the longer lever.

(Scrum-halfs generally have short levers, but make up/compensate for the lack of lever

length through muscle mass and efficient technique. The pass off the ground can bedone with a greater resistance arm if the scrum-half adopts a wide base of support and

places the ball near the back foot, thus maximising the swing distance.)

Generally then we can assume that:

SHORT LEVERS:EASY TO CONTROL, BUT LACK SPEED AND LENGTH OF

PASS (UNLESS EXTRA STRENGTH AND MUSCLE MASS IS APPLIED.)

LONG LEVERS:HARDER TO CONTROL, GENERATE MORE SPEED ANDLENGTH OF PASS, BUT CAN BE SCRAGGED BY THE OPPOSITION IN THE

PROCESS OF PASSING.

Torque & RotationTORQUE:


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Torque basically means a turning or spinning force. The speed of the torque is

determined by how much and how far from the GOG force is applied (an eccentric

force.) (Torque = FORCE (F) x DISTANCE (D)

For the scrum-half this has two main effects:

Firstly, the scrum-half himself generates torque as he rotates the arms to initiatethe back swing and then the forward swing. The heavier and longer the lever

being used (i.e. arm length and swing length) the greater the torque, as the mass of

the ball is further away from the body, causing a more powerful turning effect.

Secondly, the ball can have considerable torque (either deliberately oraccidentally) when passed, depending on how far from the COG it is held by the

controlling hand (the hand at the back of the ball.).

ROTATION:

When passing, the scrum-half needs to be careful not to over-rotate about the verticalplane. By letting go of the ball too late and over-rotating, the result can be that the ball

goes too high. The scrum-half can minimise this rotational effect by adopting and

maintaining a low body position prior to, during and immediately after the pass.

Similar over-rotation on the horizontal plane results in a horizontal curved ball path,

which is harder to control and less accurate when aiming for a specific target (i.e. in front

of the receiving player.) This is probably the most common mistake made by scrum-halfsand usually results from poor/inefficient footwork and placement.


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Inevitably a mixture of both rotations is used when passing off the ground. This is called

ELIPTICAL ROTATION, as the scrum-half needs to lift the ball off the ground(vertical) and then impart spin (torque) to the ball to speed the pass up (horizontal).

A pass that is consistently efficient (i.e. it stays straight and on-line to the target

throughout flight) will utilise a very flat vertical rotation (i.e. the arc of a wide circle) and

will try to eliminate as much horizontal or elliptical upper body movement as possible.

The diagrams below (A and B) take a birds-eye view on the path of the scrum-halfshands when passing. The hand path in diagram A is following a tight arc and this means

that the optimum release point for a straight flight path (#2) is very precise and quick.

This means the potential for releasing a less accurate pass (#2 too early, or #3 too late andbehind the target) is markedly increased. This type of rotation occurs when too much

upper body horizontal rotation is applied to the pass (usually a result of poor foot

placement).


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Diagram B clearly shows a flatter arc of movement taken by the hands and as a result the

optimum release points are more spread out. Thus, the passer is passing down the line ofaim longer, resulting in greater accuracy. A useful comparison is the greater accuracy of a

rifle compared with a hand gun, as the rifle has a longer barrel and the bullet remains ontarget longer before it is released (exits the barrel). The potential for accuracy is increased

and, even if the ball is released too early (1) or too late (2), the pass is closer to the

desired target (2) that in diagram A due to the flatter passing arc.


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This example of rotation can easily be used with FORCE SUMMATION to educate the

scrum-half (or coach) into understanding the technical aspects of the skill and evaluating

inefficient technique. The principles can easily be adapted and adopted for other skillssuch as general passing, kicking (especially place and drop kicks) and hookers throwing

in (etc).

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