To score a goal, the ball must pass completely over the goal line between the goal posts and under the crossbar— Laws of the game.
When Frank Lampard struck a beauty from outside the box against Germany at the FIFA World Cup in 2010, the whole world thought England had equalised.
The ball hit the underside of the crossbar, bounced over the goal-line and came back out before Manuel Neuer collected it. But the linesman, who is responsible for such decisions did not signal it as a goal. The score remained at 2-1 and England went on to lose 4-1.
The whole issue is not only about goals being scored, it is also about goals which are given when the ball HAS NOT crossed the line.
Mr. Lampard was involved in another example which made calls for technology stronger. In a match where they were trailing by a goal against Tottenham Hotspur, his shot wriggled through the legs of the goalkeeper, who pulled it back just in time to prevent the ball from crossing the line. But the linesman gave the goal, Chelsea equalised and went on to win 2-1. Chelsea were lucky against the Spurs again in the FA Cup.
So what does goal difference bring to the game? Will it change things for the better?
HUMAN ELEMENT ARGUMENT
"Goal-line technology will lead to Playstation football"— UEFA Chief Michel Platini.
"Other sports regularly change the laws of the game to react to the new technology. ... We don't do it and this makes football an international laughing stock"— Sepp Blatter.
Before high profile incidents, the case over technology interfering with football was closed. FIFA and the International Football Association Board had conducted tests at junior levels and still remained against the decision.
Certainly the romance with football includes heated discussions over whether a goal went in or not. AC Milan fans will constantly argue that in a top-of-the-table clash last season, they had scored a goal which would have doubled their lead against Juventus. But it was not given and Juventus tied the game 1-1 to end the season unbeaten, therefore winning the league.
Turkey will argue they scored against Brazil in the World Cup and their player was adjudged offside when he was not. Would Brazil have won the cup that year?
With goal-line tech now introduced, debates like these will all be settled with the blink on an eye. Fans who have benefited from bad decisions will wonder whether karma will come back and bite them, while fans who have been bitter will hope they get to walk on the sweet road of redemption.
LESS CONTROVERSIES ARGUMENT
If it's a goal, it's a goal. It is as simple as that.
But without technology, a can of worms is opened every time the ball 'almost' crosses the line or the goalkeeper covers the referees view in his attempt to desperately save a shot.
As Blatter himself said: "That Lampard goal was the moment for me to say 'you are the president of Fifa and you can't afford for something similar to happen in the next World Cup'."
And for a man who has a record for saying strange things in public, he is right.
A football player just cannot be denied a goal when he has scored it. Similarly, a goalkeeper cannot be adjudged to have conceded when he has not.
There are lots of other things to debate— freekicks, offsides, penalty decisions, red cards etc.
But as the saying goes: Football is like life - it requires perseverance, self-denial, hard work, sacrifice, dedication and respect for authority... and the authority now is goal-line tech.
HOW DOES IT WORK?
Hawk-eye: Already used in tennis and cricket, the hawk-eye is a proven technology. Half a dozen high-speed cameras at both ends of the stadium will track the ball and a computer calculates where the ball is. Whenever the ball crosses the line, it will send an electronic message to a watch-like receiver worn by the referees. There might be a problem when the keeper's body covers all of the ball at times.
Goal-Ref: Uses magnetic fields to detect whether the ball has crossed the line. Three magnetic strips are placed inside the outer lining of the ball, between the bladder and the outer casing. When the ball crosses the line these are detected by sensors inside the goalposts and crossbar. A bit of a complication, but no worries about keepers covering the ball.
The sensors send out electronic waves which are disturbed if the ball crosses the line. The referee will immediately know.
The major problem is how to get those magnetic strips inside the ball without them being damaged.