Cricket and the Duckworth-Lewis Method

by A.D Paterson on 06/11/2010

Cricket has many baffling rules and, for the legion of avid followers of One Day International’s (O.D.I) Cricket and 20 overs Cricket (Twenty20), there aren’t many that are as difficult to get your head around as the Duckworth-Lewis (D/L) Method. So what is the Duckworth-Lewis Method?

In this article we’ll have a look at how the Duckworth-Lewis Method got started, what their complicated formula does, and finally, whether it actually seems to work.

The creation of the Duckworth-Lewis Method

Although Cricket is a summer sport, it tends to be played in a lot of countries where summer doesn’t necessarily mean that it’s going to be hot, sunny, and above all, rain free.

Because Test Cricket can be played over anything from 3-5 days (with the finishing deadline given before the match starts) little things like rain delays just add to the fun, tension, and more often than not, draw.

In One Day International’s and Twenty20, where the games are played out over a day, there would be a definite advantage if one side batted first, added a huge number of runs, and then the second side to bat had to score the winning runs with less overs.

Oddly enough, even though One Day International’s started to gain popularity in the 1970’s, there was no definitive system in place to recalculate rain affected games until the D/L Method was first used in 1996/97.

Frank Duckworth, MBE, and Tony Lewis, MBE, were the two mathematicians who devised the system that was eventually taken up by the International Cricket Council in 2001.

How does it actually work?

There have been a number of revisions of the system over the years, and the introduction of Twenty20 has caused a number of rethinks, but essentially it goes like this:

To start with both teams, in an O.D.I, must face twenty overs before the game is classed as being a match. That means that one team could bat out their whole 50 overs and the match be classed as void if the second team only manages to bat 19 overs and 5 balls (each over being 6 balls long with the exception of overs including wide’s and no-balls).

For a Twenty20 match, where each team faces 20 overs each (assuming ‘additional’ overs aren’t bowled due to the extra deliveries needing to be bowled for wide’s and no-balls), the number of overs that must be faced before the game is an actual match is 5 overs each.

If the first team to bat doesn’t complete their allotted number of overs due to a rain delay then the D/L Method is used to work out a projected number of runs that the team should have got if they had been able to complete all of their overs.

Past matches were analysed that showed there was a correspondence in the games between the number of balls left to be bowled and the number of wickets in hand. The more wickets in hand, and balls to be bowled, the more runs a side would be likely to add before the game had come to a ‘natural’ conclusion.

These statistics were turned into a percentage which could be applied to either increase the projected score, or reduced the score and overs, as required.

For instance, one team may have completed all 50 overs and the second team be hit with a sudden downpour after batting out their first 20 overs. They have wickets in hand (and get past the point where the Duckworth –Lewis Method comes into play; which is often if the match is delayed for more than 30 minutes) so a new number of runs required, and deliveries to get them in, is calculated.

If the game resumes, and then stops again, the side batting will know how many runs they need to have by x number of overs so that they can win the match even if they don’t have to come back on the field again. If a wicket falls, the number of runs needed to win in x number of overs increases.

If the team is bang on target and the rest of the match is washed out, then it’s a tie. If they are below the number of runs required when they go off and the game is washed out, they lose.

Does this method actually work, and is it fair?

Statistically the Duckworth-Lewis Method is pretty accurate when compared with past completed matches, though many people would argue whether it’s fair.

There have been many games where the D/L Method has come into play and the side batting second have had the number of runs required to win reduced by maybe 3 or 4, but the number of overs to get them have also been reduced by 2 or 3. That means (potentially) 12 to 18 deliveries less to get them in.

So often the balance in the reduced number of runs when compared with the reduced number of deliveries seems to be a little unfair – depending on which team you’re supporting at the time, of course.

In Twenty20 where there are fewer overs and generally fewer runs scored, some of the alterations made using the Duckworth-Lewis Method don’t seem to make sense.

For instance, in one World Cup Match England had scored a creditable 191 runs for 5 wickets in their 20 overs; then the rain started after just 2.2 overs of the West Indies chase. At the time they had scored 30 without loss. The D/L method then set the West Indies a target of 60 runs in 6 overs, and they did it with one delivery to spare.

There we have it, a brief look at what the Duckworth-Lewis Method is and how it works.

Both teams have to complete at least 20 overs each in an O.D.I, or 5 overs each in a Twenty20 match of it to be an ‘actual’ game.

The D/L Method adjusts the scores up or down (overs are only adjusted down) based on the number of wickets the team has in hand and number overs they have left. The percentage used is based on historical data from other matches at similar positions in their games.

Finally, not everything in Cricket is fair, which begs the question of where the phrase ‘It isn’t Cricket’ to describe something that isn’t fair, came from.

Will knowing a little bit more about the D/L Method help to increase your enjoyment of Cricket?

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{ 13 comments… read them below or add one }

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