Can a tennis ball be in without touching the line?

Question

[Yes, I know the ball can be in without touching the line if it’s on the inside, just couldn’t think of a better, succinct title.]

Currently, the Nordea Open clay tournament is being played in Båstad, Sweden. They have a Hawkeye challenge system in place, of the ‘real bounce’ type where you see a super-slow-motion black-and-white shot of the ball landing, recorded by an actual camera, rather than just computer graphics.

A couple of days ago, I was watching a match (I think it was Albot vs Rune, but I’m not sure), and one of the players challenged a close call.

The slow-replay showed quite clearly that even at the maximum point of contact – when the ball is compressed the most vertically and has its widest horizontal area of contact with the ground – no part of the ball actually touched the line. It was equally clear from the side shot, however, that the ‘outermost’ part of the ball as a whole was right above the very edge of the line.

In other words, if viewed from above, the circular outline of the ball would obscure perhaps a millimetre of the line; but when viewed from the side, you could see that the part that obscured the line was not in contact with the ground.

Based on the slow-replay, I assumed that the ball would be called out, but it was in fact called in, and the simplified graphic showing the outline of the ball and the line showed the ball as just obscuring part of the line (as if seen from above, not the side).

All references I can find, such as Official Tennis Rules, specifically mention the ball touching or hitting the line, which in this instance it did not.

So on what basis was the ball called in by the VAR system here, then? Does ‘touch’ in practice actually refer to obscuring from above (whether or not there’s physical contact)?

Answer 1

No

For a ball to be in, it must actually touch the line. Being above a portion of the line at point of maximum impact is not sufficient.

As you rightly mention, the rules are fairly clear. From the 2021 Friend at Court document:

If a ball touches a line, it is regarded as touching the court bounded by that line.

Similarly from your source (though I don't know how official it is, regardless of the name of the website):

If a ball touches a line, it is considered to be the same as hitting the space inside that line.

Contrast this with association football, in which the relevant rule is:

The ball is out of play when it has wholly passed over the goal line or touchline on the ground or in the air.

Of course, a major difference is that in tennis we consider only the moment when the ball hits the court, whereas in football a ball can go out of play high in the air. Regardless, a similar rule for tennis could be along the lines of "If a ball is not wholly past a line when it touches the ground, it is regarded as touching the court bounded by that line". As this is not the rule, I argue the actual rule is clear in requiring the ball to physically make contact with the line.

You mention that the graphic system showed the outline of the ball. It shouldn't. A Hawk-Eye-like system is supposed to (attempt to) show the part of the ground that has come into contact with a ball. This also explains the sharp oval shape of the output of Hawk-Eye, as the area of the ball touching the ground first increases and then decreases, all the while the ball moves forward. See for example here for a short discussion and demonstration of this effect. Note that this is also different from showing the area touched by the ball at point of maximum contact.

So why was the ball called in?

Being unfamiliar with the specific game, I see a couple possibilities for why the call in a situation as you describe it might be called as in:

1. The ball touched the line. This might seem silly, but if even some of the extending fibers (or hairs) of the ball touch the line, it is technically in. This can be very hard to see.

2. The referee was wrong. Referees are human, and as all humans do make mistakes all the time.

3. The automated system was wrong. Hawk-Eye has some error rate. Although it is likely a lot better than humans at determining in real time whether a ball is in or out, it is not capable of sub-millimeter precision.