Study raises fallibility of Hawk-Eye tennis line-calling system

The Hawk-Eye line-calling system used at Wimbledon may not be quite as accurate as people think.

[Jack Howard]

The hawkeye is wrong. A tennis ball is a sphere, not a disc or hockey puck. When a replay shows the edge of the ball just over a line, the ball is out by just under the radius of the ball. The center of the ball is always the first part of the ball to touch the court. No matter how the ball is distorted by spin, the edge can never be the first part of the ball to contact the court regardless of what direction the ball is coming from. Please explain why no one seems to recognize this obvious fact.

[Freddy]

This fact is not as obvious as Jack Howard may think. Yes, the image of the ball clipping the line is really the ball when it flattens momentarily as it hits the surface. Nevertheless, how MUCH the ball flattens would depend on hard it was hit, the angle whence it came, whether it was flat or with spin. Too many variables. Yes it is less than precise but it certainly is more reliable than the human eye. Clay court tournaments do not use it because the ball leaves a mark and organisers feel that that is a better indicator of whether the ball is our or not. Fair enough. But on hard courts and on grass, hawkeye is decidedly the better option.

[Den]

I thought the same as Jack did until someone told me the dark shadowed image in the replay actually represents only the surface of the ball touching the court, not the entire ball. I recently recorded some of the US Open just to stop the action of a replay longer than they do on TV and sure enough, the dark spot relative to the line is much smaller