How does Duckworth-Lewis-Stern or DLS Method work in cricket?

 Cricket's Duckworth-Lewis method: rules, methods, and calculations during rain-shortened limited-overs matches.

How does the DLS work?

The Duckworth-Lewis-Stern method or DLS method (as it is now known) is a mathematical method employed to calculate target scores and reach outcomes in rain-shortened limited-overs matches. Initially named after English statisticians Frank Duckworth and Tony Lewis, it was first used in 1997. A formula was updated by Australian academic Steve Stern, who was named its custodian ahead of the 2015 World Cup.

What is the purpose of it?

Despite being an ideal solution, implementing a reserve day for limited-overs matches is not always possible due to logistical and scheduling challenges. As a result, game administrators have long been searching for the fairest way to determine outcomes for rain-affected one-dayers. When inclement weather interrupts a match and teams are unable to complete their full number of overs, a calculation must be made in order to reach a resolution within the time available. This calculation aims to adjust the target score based on the reduced overs, but it is ultimately an estimation without one definitive answer. In order to account for various variables and accurately reflect the efforts of both teams, the ICC has developed a formula that has been updated several times and is widely regarded as the most precise system used in international cricket: the DLS method.

DLS's journey has been just as interesting as the rule itself. If we dig deeper into the history of ODI cricket, we find out that the Average Run Rate or ARR method existed as soon as ODI cricket began. It was easy to calculate the Average Run Rate based on the run rate. However, soon players realized that it would be more beneficial to the team second and that something more important must be substituted.

With this rule, the batting second team target is not decided based on the overall run rate of the team that batted first, but based on the specific run rate of the overs in which the former team scored the most runs.

This rule, however, favors the team bowling second and cannot be relied on much. When no better alternative could be found, the DLS method was introduced.

What is the DLS method?

Neither the ARR nor the MPO methods took into consideration the remaining wickets of a team, ignoring a crucial aspect of the match situation. However, the DLS method addresses this issue by factoring in both overs and wickets as valuable resources, ultimately revising the target based on their availability. At the beginning of an innings, a team has 100% of its resources (50 overs and 10 wickets) at hand. The DLS method measures the remaining balls and wickets as a percentage throughout the match. To determine the value of each wicket or ball in percentage terms, a formula is used that considers scoring trends in international matches over a four-year period (ODI and T20, for both men and women). Every year on July 1st, new data is added to this formula to keep up with evolving scoring patterns.

Over the course of an innings, resources deplete at an exponential rate, with the percentage of resources falling faster as more wickets are lost and more balls are consumed.

Assuming equal resources are available to both teams, the DLS method calculates how many runs teams should score (and would have scored) if the resources were equal. In international cricket, resource values (which are not publicly available) are obtained from a computer programme. To calculate a target, the formula is as follows: Team 2's par score = Team 1's score x (Team 2's resources/Team 1's resources).

The DLS method takes into consideration the potential changes in batting strategy caused by rain interruptions. The weighting of wickets and overs is determined by a formula, which cannot account for the individual batting abilities of players. It has been observed that under this method, teams often opt to conserve wickets in anticipation of rain, even if it means a slower run rate. In an effort to address this issue, Steve Stern made adjustments to the formula to better reflect the current trends seen in high-scoring ODIs and T20 matches.

In an older version of the DL method (called D-L Standard Edition), resource values are precalculated from charts and used when computers are not available. A quantity called the G50 — the average total score in 50-over innings — is used to make upward revisions (when the first innings is interrupted). As of now, G50 is fixed at 245. However, international cricket does not use the Standard Edition.

What was the first time the DLS method was used?

As a result of the efforts of Frank Duckworth and Tony Lewis, the DLS method was created to provide a better alternative to rain affected cricket matches. On January 1, 1997, Zimbabwe and England used the DLS method officially for the first time. In 1999, the ICC officially adopted the DLS method as a rain-affected game calculation method.

Global adoption and impact of DLS

DLS has become the go-to solution for settling one-dayers affected by rain. It has been adopted by the International Cricket Council (ICC) and is widely used in cricket matches.

In the face of unpredictable weather conditions, the DLS method plays a crucial role in maintaining the integrity of limited-overs cricket by ensuring fairness and accuracy.

The Duckworth-Lewis-Stern method has transformed the way rain-affected matches are decided and also represents the innovation and collaboration of cricket statisticians in ensuring fairness and competitiveness throughout the sport.