The server must stay within the service zone until the ball crosses the short line.

The ball must cross the short line on each serve.

If the ball does cross the line a radio signal is sent to the referee's watch within a second.

Today, it was worth $400 each time the ball crossed the net.

But officials ruled that the ball did not cross the goal line.

But the ball could not physically cross between the frames.

Altogether, the ball crossed the net more than 12,000 times.

The ball left his hand and crossed the goal line.

Television replays showed the ball had indeed crossed the line.

This film material appears to show that the ball did not cross the goal line in full.