At altitude the ball stops behaving and nobody warns the players

Thin air removes both drag and spin effect, which turns a controlled topspin game into a series of balls flying long.

Play a tournament two and a half kilometres above sea level and the equipment is identical, the court dimensions are identical, and the sport is not. Air density falls with altitude, and almost everything interesting about a tennis ball's flight depends on air density.

Two things happen at once. Drag falls, so the ball keeps its speed and travels further before gravity brings it down. And the aerodynamic force generated by spin falls with it, because that force also comes from the air, so the topspin that a player relies on to drag the ball down inside the baseline delivers less. A player whose shot lands two feet inside the line at sea level now watches the same swing sail. The instinctive correction, more spin, works less well than it does anywhere else, which is a cruel arrangement.

Events at altitude respond by using a different ball, one with a heavier core or a different pressure specification, and it helps. It does not eliminate the problem, because the ball is only half the equation and the air is the other half.

What this produces tactically is closer to old fashioned tennis than anything on the regular calendar. Serves are enormous. Rallies are short. The player who can flatten out a shot and take the ball early does well, and the grinder who wins by hitting a heavy loopy ball twenty times has lost their entire method. The reverse case, low altitude and thick humid coastal air, produces the opposite. Heavy conditions, the ball dies, spin bites hard, and the grinder is at home.

I find it odd that this variable gets almost no attention from a sport that talks endlessly about surfaces. A hard court at altitude and a hard court at sea level are labelled the same in the record books and play about as differently as clay and grass. Ranking points are identical. Nobody adjusts anything.

Which is a wasted opportunity, because it would explain results that currently get filed under form. A specialist who wins repeatedly in thin air is not lucky and is not a fluke. They have adapted to a physical condition that the schedule treats as invisible.

Look at where the tournament sits before you look at the draw. It tells you more than the surface label does.