I've just read about 'Hawkeye'. You may be correct in that tennis analogy. Just read about it. I think Hawkeye measures the impact point of the ball. But can anyone say that in football they have ever assumed that the 'impact point' of the ball constitutes a 'whole' as in 'wholly' crossing a line?I am not sure if your statement is correct, for tennis or for football. In below image, to the right is in field, to the left is out of field. Viewing from above there is no daylight between ball and line. In football it is in play, in tennis it is out of play.
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