New balls are a different game and we pretend otherwise

A ball changes measurably within a few games, yet tactics, statistics and commentary all treat it as a constant object.

Two things happen to a tennis ball once it is in play. The felt fluffs up, which increases drag and makes the ball slower through the air and easier to control, and the internal pressure drops slightly, which takes some of the life out of the bounce. Neither effect is subtle by the standards of a sport where a few centimetres decide points. Both happen within the first handful of games.

So the same player, hitting the same shot with the same intent, is playing a different physical problem at two all than they were at love all. Flat hitters get the worst of it, because a slower ball through the air gives the opponent time and the flat hitter has no spin margin to fall back on. Heavy topspin players get a small gift, because a fluffier ball grabs the strings better and a slower flight is not really their concern anyway.

You can see this in the shape of a set if you know to look. New balls tend to produce shorter points and more free serve points for a game or two. Then the rallies lengthen. Commentators explain that as a player settling in, which is sometimes true and is often just the felt doing its work.

What genuinely surprises me is how little this shows up in tactics. Everybody knows the ball change is coming. Almost nobody plans around it. If I were coaching a returner facing a big server I would want them treating the two games before the change as the window to attack, because that is when the server has the least free help from the equipment, and it is also when the server is most likely to be pushing for pace they cannot quite produce.

The honest complication is that ball behaviour also depends on the court and the altitude and how long the tin sat in a warm storage room, and none of that is published or standardised in any way a player could plan around.

Which is the real point. We measure serve speed to the kilometre and we do not track the state of the object being served.

That is a strange set of priorities for a sport this obsessed with numbers.