Duckworth–Lewis–Stern (DLS) Fundamentals

In this lesson you will learn why a special method is needed when a limited-overs match is interrupted. Imagine the side batting first makes one hundred and sixty in twenty overs, then rain cuts the chase to twelve overs. What is a fair target? Simply scaling by overs, giving a target of ninety-seven, ignores the fact that the chasing side still has all ten wickets to use in fewer overs, which makes aggressive batting much less risky. Older methods based only on run rate often produced unfair results. The Duckworth–Lewis method, later updated by Professor Steven Stern and renamed Duckworth–Lewis–Stern, was developed to address this problem in a fairer way.

• Interruptions can reduce overs available
• Scaling by overs alone is often unfair
• Wickets in hand matter as well as overs
• DLS was developed to set fairer targets

In this lesson you will learn the key idea behind DLS: resources. A batting side has two resources with which to score runs, the overs remaining and the wickets in hand. At the start of an innings, a side has one hundred per cent of its resources. As overs are bowled and wickets fall, the resources remaining go down. Losing a wicket early reduces resources far more than people expect, because it limits how freely the side can bat. DLS uses tables, or software, built from a large amount of match data to say what percentage of resources remains for any combination of overs left and wickets lost. Revised targets are then based on comparing the resources available to each side.

• Two resources: overs remaining and wickets in hand
• An innings starts with 100 per cent of resources
• Resources fall as overs pass and wickets fall
• Tables or software give resource percentages

In this lesson you will learn two terms you will often hear. The par score is the score the chasing side would need to have reached at a particular point to be level with the side batting first, given the resources it has used. If play is ended and the chasing side is above par, it wins; if it is below par, it loses; if it is exactly on par, the result is usually a tie, subject to the playing conditions. A revised target is the new target set when overs are lost, normally the par score for the full revised innings plus one. These figures must come from the authorised calculation. You should never estimate them and announce them as official.

• Par: the score needed to be level at that point
• Above par wins; below par loses
• Revised target is normally par plus one
• Never estimate and announce figures as official

In this lesson you will learn that there are different versions of the method. The Professional Edition is computer-based and is used in international and professional cricket. A Standard Edition, using printed tables, has been available for situations where software is not, and some scoring apps include a DLS calculator. Which version applies, and whether DLS is used at all, is set by the competition regulations, not by the scorer, the umpires or the captains on the day. The figures from different versions may not be identical, which is another reason why you must only use the authorised method named in the WFA competition regulations.

• Professional Edition: computer-based
• Standard Edition: printed tables
• Some scoring apps include a DLS calculator
• The competition regulations decide which applies

In this lesson you will learn the information scorers must have ready when play is interrupted. Any revised target depends on accurate records, so note the exact score, wickets lost and overs bowled, to the ball, at the moment play stops. Record the time play stopped and the time it restarted. Record the number of overs the umpires confirm for the revised innings, and any change to the maximum overs per bowler or to the powerplay. If the first innings was interrupted, record exactly when and how many overs were lost. Your accuracy here is crucial: a one-ball error in the overs bowled can change a revised target.

• Exact score, wickets and overs at the stoppage
• Times play stopped and restarted
• Revised overs confirmed by the umpires
• Changes to bowler limits or powerplay

In this lesson you will learn how the scorer and umpires work together after an interruption. The umpires decide when play resumes and how many overs remain under the playing conditions. The revised target is then calculated using the authorised method, and scorers often assist by entering the figures into the approved software and cross-checking them with the umpires. Agree the revised target, the revised overs and any changes to bowling limits before play restarts, and make sure both captains are informed. Display the new target clearly on the scoreboard. If there is any disagreement, the umpires and the competition regulations decide, not the scorers or the teams.

• Umpires decide resumption and overs remaining
• Targets come from the authorised method
• Agree figures before play restarts
• Inform both captains and update the scoreboard

In this lesson you will learn that a result under a revised target is only possible if enough overs have been bowled. Competitions set a minimum number of overs that each side must face for a result to stand. In standard international twenty-over playing conditions this is five overs for each side, but other competitions may use different figures. If the minimum is not reached, the match is usually declared a no result. In the Winn Family T-20 League a no result is worth one point, but always check the WFA competition regulations for the minimum overs and how interrupted matches are decided. Record the reason for any no result clearly on the scorecard.

• A minimum number of overs is needed for a result
• Standard international T20 minimum: five overs each
• Below the minimum is usually a no result
• WFA no result: one point; check the regulations

In this final lesson you will reflect on the limits of what you have learned. You now understand why DLS exists, the idea of resources, the meaning of par scores and revised targets, and the information scorers must record. You have not been trained to calculate official targets by hand, and you should never do so in a real match. DLS is a detailed method maintained by the authorised providers and applied through approved software or tables, under the rules set by each competition. Treat this module as an introduction. For any real decision, use the authorised calculation, follow the WFA competition regulations, and agree everything with the umpires.

• This module is an introduction only
• Never calculate official targets by hand
• Use the authorised calculation and software
• Follow the WFA competition regulations and umpires