Most sports keep score with a table. Teams accumulate points across a defined season, the table resets, and the standings describe what has happened since the last reset. Tennis works differently, and the difference explains a great deal about why players schedule the way they do, why an injury is more damaging than the missed matches alone suggest, and why a ranking can fall during a stretch of winning tennis.
The professional tours rank players over a rolling window rather than a season. Nothing resets. Each week the list is recalculated over the preceding fifty-two weeks, which means a ranking is not a record of a career or even of a year. It is a snapshot of a moving twelve-month period, and every result inside it has an expiry date known in advance.
