Losing early wickets and chances of victory

I have a general hypothesis which I will be exploring throughout a series of blog posts in this season, and it is this: batting teams start with two resources (balls and wickets), and they spend those resources as efficiently as possible to convert them into as many runs as possible. Thus Twenty20 cricket isn’t just about scoring runs as fast as possible. You want to preserve enough of your wickets to be able to play a riskier game at the tail-end of the innings “spending” those surplus wickets to give you the capacity to score at a faster rate.

In today’s post, I want to explore the role of losing early wickets in determining how many runs a team scores, and their chance of victory.

As a taste, this graph shows the likelihood of victory for teams based on how many wickets they have lost after five overs:

wicketschance11.png

Teams that have maintained all of their wickets have roughly two-thirds chance of winning. Teams that are down one wicket are still favoured to win, but the chance of victory drops gradually further. A team which has lost four wickets has less than 20% chance of winning. There have only ever been six innings where a team had lost six or seven wickets after five overs, and in all six cases that team went on to lose.

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Win probability after the first innings

Yesterday afternoon I went to North Sydney Oval to watch the Renegades play the Strikers in the second WBBL game of the season. Yesterday’s post had pointed out that no team had won a domestic Australian women’s T20 match since 2009/10 after having been bowled out.¬†When the Strikers were bowled out for 116, I pointed out this stat, but I was also aware that 116 was a relatively good score for a bowled-out team and likely more than most other cases of teams who lost all of their wickets.

The Strikers went on to win with relative ease after bowling out the Renegades, making it the first match in women’s domestic T20 in Australia since 2009/2010 where the team batting first lost all of their wickets and went on to win, and also the first match since at least 2009/10 where every single wicket was taken.

To help understand these chances of success, I have calculated the probability that a team batting first will win based on their score at the end of their innings. The following charts show these statistics for both men and women (although it’s worth noting the volume of data is much greater for the men).

halftimewinchanceF.png

To take the three matches played yesterday as examples:

  • The Perth Scorchers scored 119 in their first innings in the morning game. Teams scoring 116-120 won 49.4% of the time, and lost 47% of the time. Based on this, you would expect a very close contest, with Perth having roughly 50% chance of victory. We got a close result, with the Hurricanes defeating the Scorchers with an over and 5 wickets to spare.
  • The Adelaide Strikers recovered from an early collapse to score 116 after losing all of their wickets. This fell into the same category as the Scorchers innings, but the Strikers went on to win with ease after another batting collapse by the Renegades.
  • The Melbourne Stars performed strongly in the evening game, scoring 147. Women’s teams scoring 146-150 went on to win in 75% of cases, and so did the Stars – although the Thunder did well to come within six runs.

halftimewinchanceM.png

I might update these charts from time to time – at the moment they use data up to 22 November.

You can look at the data yourself here if you want to check the exact proportions, and see how many match results are included in each category.

There’s a lot more to be said about win probabilities – things get more complicated when you look at points midway through the first or second innings, at which point you also need to factor in wickets lost. I will definitely be returning to this point, but for now you can get a good sense of the likely result at the halfway point.