How Does DLS Work in Cricket?

The Duckworth Lewis Stern (DLS) method in cricket is a way to decide a winner in a game where rain meant not all the scheduled overs could be played. It can either set a revised target for the team batting second or decide a winner after a game is abandoned.

To understand why DLS is useful, imagine a 50-over one day game where the first team scores 300 runs in 50 overs (six an over) and then a rain delay means the second team only has 25 overs to bat. It might seem logical to simply reduce their target proportionally, meaning 150 runs in 25 overs (still six an over). However, this is unfair for two reasons:

• The team can bat much more aggressively and take more risks because only batting for 25 overs compared with 50 means much less chance of being bowled out.
• The team has a big advantage by knowing it has this reduced target. Contrastingly the team batting first did so assuming both sides would face 50 overs.

The DLS method appears complex in practice, but is simple in principle. It’s based on the idea that a batting team has two resources that allow it to continue batting: the number of wickets remaining and the number overs remaining. If either of these resources runs out, it will no longer be able to bat and score more runs.

The simpler edition of DLS, often used in local club games, uses a table that cross references wickets remaining and overs remaining to give a percentage figure. The figures aren’t completely proportional because, for example, the first few wickets of an innings (the specialist batsman) are treated as much more valuable resources than other wickets. They also take into account that teams usually score more quickly at the start of a game (using their best batters) and the end of the game (when the risk of losing wickets becomes less important.)

In our example, the team batting second has all of its wickets remaining and half of its originally scheduled overs remaining. The table shows it has having 66% of its total resources remaining, so the target will be 66% of the first team’s score of 300, meaning 200.

The professional version of DLS runs on a computer. It’s the same principle, but uses more detail, based on actual records of previous games. In particular, it takes account of the fact that professional and international teams tend to score at a higher rate than amateur and club sides.

While the principle is always the same, the use of DLS changes slightly depending on when the rain delay happens and whether it affects both sides (and to what extent.) The key remains that the target scores take account of the effects of having fewer overs to score but the same number of wickets remaining (plus the benefit of knowing about the reduced target).

DLS is not used in first class matches such as Test matches. In these matches, rain delays are considered part of the game and contribute to the possibility of a draw. Judging this risk and deciding when to declare is part of the tactics in first class cricket.