When you head a soccer/football, you must hit it with more force than the ball has - transferring your energy to the ball rather than your own head. This is the same as with headbutting someone in the head. The aim is to make the energy hit the back of their head. This, combined with the angle and the part of the head you use allows you to head a soccer/football with minimal damage.

Perhaps a physicist could elaborate.

As true as it seems with footballers and their thick skulls, it is not a necessity :P

The dissyness is caused by your brain hitting the front of your skull when your head rocks back on being hit by the ball.  This is also the cause of damage during boxing.  To reduce it, it is important to keep your head as steady as possible and that means practice and building up strong muscles.

Local bruising is different, this will be worse if you do not go with the blow, but the pain is less depending on the area of your head that gets hit.  If you think of your head as a cube, the front corners are usually less painful to hit and if the ball scuffs you (slides over the top or side of your head) this might tear some skin, remove some hair and of course hurt.

the answer is simple techinque..... look at professional footballers and you will see that they rarely ever just headbutt a ball( unless they are diving into it etc), usually what happens is that they momentarily cock their heads backwards at the moment of impact ( thus lessening the impulse of the blow) before bashing the ball in the prefered direction, they also tend to use the flattest part of the skull because , well its easier to bounce sumn of a flat surface... also another thing to consider is that during heated matches with the adreniline rush and enorphin surge , pain becomes a dull concept , only the action of the moment matters

The effect is related to other athletic feats like breaking wooden planks with a karate chop.  Elements of the body are linked in what is called in biomechanics a 'kinetic chain' - the athlete increases the effective mass of the head in the collision by stiffening the neck muscles to This has two useful effect. First, it adds some fraction of the body mass to the effective mass of the head in the head/ball collision - this causes the ball to bounce back fast in the desired direction instead of stopping dead (as happens when two similar-mass objects collide, like snooker balls).  Second, the stiff neck prevents the skull from snapping backwards and hitting the brain which is floating inside of it.

Imagine you were able to head a stationary ball to the goalkeeper from where you were standing that day. The force your head would have to exert on the ball would be equal in magnitude to the force exerted by the keeper kicking the ball. Since the ball exerts an equal reaction force on your head, it would be as if the keeper had kicked you in the head. Consider yourself lucky to just end up with a bruise or a headache.

In practice you would, of course, not be trying to head the ball all the way back to the keeper, but there are other things to consider with a falling ball. Ignoring air resistance, a football dropping vertically from 20 metres would hit the ground at a speed of nearly 20 metres per second. If you could reverse the velocity of the ball by heading it, assuming the ball has a mass of 400 grams and is in contact with your head for one-hundredth of a second, the force you experience is around 1500 newtons - the weight of two adults.

When professional footballers head the ball, they generally apply a small force to deflect it, usually to steer it into the net. That does not require taking the full force of the ball on the head. But if that is the only option, they use their necks, backs and knees as shock absorbers. In so doing, they increase the time the ball takes to slow down. By Newton's second law - force equals mass times acceleration, or in this case deceleration - this reduces the ball's deceleration and thus the force. However, as you have found, it takes skill and experience to get the timing right.

Mike Follows, Willenhall, West Midlands, UK