Van Alen capped tennis sets with a tiebreak

Traditional tennis scoring required a set to be won by two clear games, with no cap: if two evenly matched players kept trading games at 6-6, 7-7, 8-8 and beyond, the set — and the match built from several sets — had no guaranteed maximum length. For casual club play this was a curiosity; for a televised tournament with a schedule, a broadcast window, and other matches queued behind it on the same court, it was a real operational problem no rule addressed.

The sport's instinct was to treat marathon sets as tennis working as designed — a test of endurance and nerve — rather than as a scheduling defect, and no format change had ever been seriously trialed at the top level because it meant altering the game's oldest and most identity-defining rule.

Jimmy Van Alen, developer of the broader Van Alen Streamlined Scoring System, proposed a hard stop: once a set reached 6-6, instead of continuing indefinitely under the two-clear-games rule, players would switch to a separate, bounded mini-game — an early sudden-death, best-of-nine-points format — whose winner took the set outright regardless of the two-game margin. The US Open adopted it experimentally in 1970, the first Grand Slam to do so, signaled to spectators by a red 'Sudden Death' flag raised at the umpire's chair once a set reached 6-6.

Added a bounded sudden-death mini-game that activates only at 6-6, capping set length without altering how ordinary sets are played.

The tiebreak only activates at 6-6, so most sets are unaffected.

It guarantees a maximum set length, solving scheduling.

It preserves the traditional two-game margin for the common case.

It was adopted experimentally, easing acceptance.

When a rule allows unbounded duration, add a bounded fallback that triggers only after a threshold, preserving normal operation.

Fans at the 1970 US Open reportedly received the format with enthusiasm even as several top players, including Pancho Gonzales, publicly complained about its abruptness and intensity; the format was refined over the following years into the now-standard best-of-twelve-point tiebreak and was adopted across the sport.