Defensive exercises

25 min

Stopping a ball you cannot see

A goalball defender has about a second to hear where a throw is going, get the body in the way and stop a 1.25 kg ball. Good defence is therefore about three things: being in the right place before the throw, reading the sound of the bells early, and making a long, low, safe block with the whole body. The three defenders work as a unit, talking between throws and staying silent and still while they listen. This lesson refines the defensive positions, the block, the physics of hearing direction and of stopping the ball, and the rules on defence.

Definition

Ready position: crouching or kneeling on the orientation lines, weight forward, hands touching the floor or lines, facing the thrower and listening.

Block: dropping onto the side across the path of the ball, arms stretched above the head and legs straight and together, so the body forms a long barrier.

Triangle defence: the centre player a little in front of the two wings, so that the wings cover the sides and the centre covers the middle and the gaps between them.

Sliding: moving sideways along the lines towards the sound before dropping into the block.

Illegal defence: a first defensive contact made by a player with no part of the body in the team area (Rule 27).

Interaural time difference: the tiny difference in the time a sound takes to reach the two ears; the brain uses it to judge direction.

The block in six steps

Step	Teaching points
1. Ready	On your orientation lines, low, facing the thrower, hands touching the floor; silent.
2. Listen	Track the bells from the moment the thrower picks up the ball; judge direction and speed.
3. Slide	Move sideways to put your body in line with the ball, staying low.
4. Drop	Drop onto your side across the path, arms stretched above the head, legs straight and together, body long and facing the ball.
5. Absorb	Take the ball on the body, not the head; keep the hips and shoulders forward so it does not roll over you.
6. Control and recover	Trap the ball, call so team-mates know you have it, return to position by touch, and start the next attack inside 10 seconds.

Rules on defence (Rules 14, 22, 26, 27 and 31, summarised). The first defensive contact must be made by a player with some part of the body in the team area. A blocked ball that rebounds over the centre line, or over the side line in the neutral area, is a "ball over" and is returned to the defending team. From the first defensive contact the team has 10 seconds to get the ball back over the centre line. Touching your eyeshades during play is a penalty; if a thrown ball knocks them, play continues until the ball is controlled, blocked out or scores. In a penalty throw, a single player defends the whole goal.

Worked example

Worked example 1: hearing direction. Sound travels at about $343\,\mathrm{m\,s^{-1}}$ and a person's ears are about $0.20\,\mathrm{m}$ apart. For a sound arriving at angle $\theta$ from straight ahead, the far ear hears it later by about

\Delta t = \frac{d\sin\theta}{c}

Ball 30° to the side: $\Delta t = \frac{0.20 \times \sin 30^{\circ}}{343} = \frac{0.10}{343} = 0.000\,29\,\mathrm{s}$ , about 0.29 ms.
Ball 90° to the side: $\Delta t = \frac{0.20}{343} = 0.58\,\mathrm{ms}$ .
Ball straight ahead: $\Delta t = 0$ .

The brain compares these differences of less than a thousandth of a second to judge where the ball is. When the defender turns to face the sound, the difference falls to zero, which is why defenders keep facing the ball as they slide. It is also why the court must be silent: other noises confuse the comparison.

Worked example

Worked example 2: why padding and technique matter. A 1.25 kg ball arrives at $12\,\mathrm{m\,s^{-1}}$ . Its kinetic energy is $\frac{1}{2} \times 1.25 \times 12^{2} = 90\,\mathrm{J}$ . If the body stops it over a distance $s$ , the average force is $F = \frac{E}{s}$ .

Stopped over 0.10 m: $F = \frac{90}{0.10} = 900\,\mathrm{N}$ .
Stopped over 0.15 m, with padding and a body that gives a little: $F = \frac{90}{0.15} = 600\,\mathrm{N}$ .

Spreading the stop over a longer distance, and over a large area of the body rather than a hand or the face, makes the block safer. The rules allow padding, but clothing, equipment and padding may not extend more than 10 cm from the body (Rule 5.6). Values are illustrative.

Video: "Goalball Training Video: Blocking", U.S. Association of Blind Athletes. As you watch, check the ready position, how the player drops onto the side, and where the arms and legs are at contact.

Tip

"Silent, low, long, facing." Stay silent and low, make your body long when you block, and keep facing the sound.

Warning

Common mistakes. Sitting up or kneeling upright, so the ball passes underneath. Blocking with the hands only. Bending at the waist, leaving a gap between arms and legs. Talking while the other team is throwing. Leaving the lines and losing orientation.

Safety. Wear knee, elbow and hip pads, and keep the arms in front of the face when blocking. Practise with slow throws and a softer ball before full-speed throws. If the ball strikes a player's head and she then has a headache, dizziness, nausea or confusion, suspect a concussion: remove her from play and refer her to a health worker (ERC 2025). Language matters too: talk about "players with a visual impairment", and remember that sighted pupils wear eyeshades and play on the same terms.

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Practice

Describe the ready position of a goalball defender.
List the six steps of a block.
Explain why the centre player stands slightly in front of the wings.
Calculate the interaural time difference for a ball 45° to the side (d = 0.20 m, c = 343 m s⁻¹).
A 1.25 kg ball at 10 m s⁻¹ is stopped over 0.12 m. Find its kinetic energy and the average stopping force.
A defender stands outside the team area, in the neutral area, and is first to touch the ball. What is the ruling?
A team blocks a throw; the ball rebounds over the centre line. What happens next?
A coach tells defenders to sit up so they can move faster. Evaluate this advice.

Show answersHide answers

Crouching or kneeling on the orientation lines, low, weight forward, hands touching the floor, facing the thrower, silent and listening.
Ready; listen; slide in line with the ball; drop onto the side with arms above the head and legs together; absorb with the body; control, call and recover.
So that the wings cover the sides near the goal and the centre covers the middle and the seams between them; angled throws must pass two defenders.
Δt = 0.20 × sin 45° ÷ 343 = 0.141 ÷ 343 = 0.000 41 s, about 0.41 ms.
E = ½ × 1.25 × 10² = 62.5 J; F = 62.5 ÷ 0.12 = 521 N.
Illegal defence: the first contact must be made by a player with part of the body in the team area (Rule 27).
A "ball over": the referee stops play and the ball is dropped back to the defending team in its team area (Rule 22).
Poor advice. Sitting up is quicker to move but leaves a gap under the body and puts the head and face in the path of the ball. A low ready position and a long, flat block cover more of the goal and are safer.

Quick check

Put the block in order.

Tap the cards in the right order.

Remember

Ready low on your lines, silent, facing the thrower; slide, drop long onto your side, absorb, control, recover.
Defend in a triangle: centre a little in front, wings back near the wing lines.
Direction comes from tiny time differences between the ears, $\Delta t = \frac{d\sin\theta}{c}$ , so the court must be silent.
First contact from the team area; 10 seconds to throw back; padding up to 10 cm; suspected concussion means remove and refer.

1Stopping a ball you cannot see

2The block in six steps

Stopping a ball you cannot see

The block in six steps