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I have a question about Geoff Hurst鈥檚 famous goal in the final of the 1966 football World Cup, and it鈥檚 not whether it crossed the line. His shot hit the goal鈥檚 crossbar, deflected downwards, hit the ground and bounced out, away from the goal. I have seen similar shots since. Why does a ball that hits the underside of the crossbar nearly always bounce away from the goal after it hits the ground? The more powerful the shot, the more likely it is to do this.

鈥� When the ball strikes the underside of the crossbar it acquires backspin. The crossbar exerts a turning force to the top half of the ball in the opposite direction to that in which the ball itself is moving. When the backspinning ball then hits the ground, the spin will tend to make it bounce back out of the goal and into the field of play.

This is easiest to understand if you imagine a backspinning ball dropping straight onto the ground in the goal area. The backspin would manifest itself as the ball rolling away from the goal.

The controversy surrounding Geoff Hurst鈥檚 1966 World Cup Final goal will likely be eclipsed, for a while at least, by that around Frank Lampard鈥檚 鈥済oal鈥� for England in their 2010 World Cup match against Germany in Bloemfontein, South Africa, on 27 June. Deflected by the crossbar, the ball landed behind the goal line but had enough backspin to bounce back to the underside of the crossbar. It then landed just outside the goal. This led the hapless officials to decide that the ball had never crossed the line.

Mike Follows, Willenhall, West Midlands, UK