Is the WBBL lifting women’s T20 scores?

At the start of the first WBBL season, I wrote a blog post about women’s cricket which amongst other things analysed ‘normal’ par scores in women’s T20 cricket. I returned later to do a post specifically focusing on par scores in both men’s and women’s T20 cricket.

After writing these posts, I kept an eye on WBBL scores and thought that they were beating the par scores more often than expected, and it made me wonder whether the higher level of professionalism and the inclusion of international players was meaning that the WBBL was producing higher-scoring games. This brings us to today’s post, where I’ll run through some statistics showing how the number of runs scored per innings has changed in the WBBL, and some explanations as to why. I’ll also give some evidence that this trend is not taking place more generally.

I started with this first chart. I separated out scores based on whether the team won the match, and whether they were playing in the first innings and second innings. I had issues last season with working out how to treat winners in the second innings, as they do not necessarily have the same incentive to score as fast as possible, and we don’t know how many runs they would have scored if they had batted for the full twenty overs. The chart shows the average run rate, not the average score. Multiply by 20 to get the average score.

wt20closeness2.png

(Where a team is bowled out, I calculate their run rate as if they had batted without scoring for the remainder of their overs. Where a team ceases to play because they have won the match, I don’t do this. The data dates back to the 2009/2010 season, which is the first for which I have data for a domestic Australian women’s T20 competition.)

Interestingly, you don’t see an increase in run rates for winning sides in either innings. You see a mild increase for losing teams batting first, but the big change is for losing teams batting second.

These are the teams which are chasing down a total, and in most cases will be behind in the chase. In 2009/10, the average run rate for these teams was around 4.9 runs per over, which would total 98 runs. It almost reached 6 runs per over (120 runs) in the first WBBL season in 2015/16.

So is this is a general trend, or just one in Australia? Unfortunately I don’t have a complete dataset of women’s domestic cricket in countries like England, India or South Africa (only New Zealand has as much data as Australia), but I can compare the Australian domestic women’s game with T20 internationals and the equivalent men’s events:

wt20closeness1.png

No evidence of a similar trendline in these other datasets.

My next theory: losing teams are not being bowled out so quickly, so they last the whole innings.

wt20closeness4.png

Not true! There was a significant jump in the proportion of matches ending with the second team being bowled out in 2015/16. After slowly dropping from 2009/10 to 2014/15, last season this measure jumped from 22% to 41%. It’s also interesting to discover that not a single team that lost all ten of their wickets has gone on to win their match in the last six seasons of the WBBL and its predecessors.

I also checked out the average number of wickets lost in each innings of play:

wt20closeness3.png

The number of wickets lost per innings ticked up in 2015/16. It’s also worth noting that losing performances in the second innings have consistently lost a wicket more than losing performances in the first innings, over the last seven seasons. There’s a similar trend seen in the Big Bash League.

So losing teams, particularly those batting in the second innings, are scoring more runs relative to the teams that beat them. This is happening alongside those teams also losing more wickets (particularly in the second innings), and being much more likely to be bowled out if chasing down a target.

So if losing scores are going up, and winning scores are remaining steady, what does this mean for the closeness of games? Are they getting closer? Well, yes, they are.

wt20closeness5.png

Back in 2009-2012, the gap between the winning team and losing team was usually around 1.75-2 runs per over (35-40 runs, if the winning team bats first or wins in the final over).

This slowly declined, before crashing in 2015/16, when the gap in WBBL01 was barely one run per over.

The same isn’t true in other T20 tournaments.

wt20closeness7.png

There was an improvement in close matches in the first season of the franchise-based Big Bash League in 2011/12 but there hasn’t been a clear trend since then. There are no clear trends in close matches in T20 internationals for either men or women since 2009.

(I’ll save you yet another chart, but there is also no such trend in New Zealand women’s cricket).

So what can we learn from these stats? I have two main theories which are backed up by this data.

Firstly, the move to franchises in the WBBL last season improved competitiveness in the tournament. The NSW Breakers have been traditionally dominant in state-based women’s cricket. They’ve won all but three seasons of the National Women’s Cricket League (50-over cricket) in its 21-season history. NSW had also made the final in five out of six seasons of the state-based T20 competition which preceded the WBBL. This would explain why we see a particular increase in competitiveness in 2015/16. The old state sides had much more of an uneven pool of potential players, and the ability for players from the bigger states to move to smaller states for more opportunities would have been much less for women due to the minimal pay.

But I don’t think that explains everything – since competitiveness has been improving prior to the last season. In future posts I might try to explore this question further.

 

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