Such is the nature and the speed of evolution of cricket in the current (non-pandemic) world, T20 franchise leagues are seemingly popping up in almost every corner of the globe. The rise of the franchise was started by the Indian Premier League (IPL) in 2008, with many countries following suit when they saw the success of the IPL and the elite standard of cricket that can be played when you attract the game’s best players for a condensed period of time.
Whilst the IPL is undoubtedly the strongest and most successful version of the franchise tournament, several other countries have been able to launch their own competition, with Australia’s Big Bash League (BBL), the Caribbean Premier League (CPL) and the Pakistan Super League (PSL) to name but a few. Added to that, The Hundred was, of course, all set to launch in England and Wales this year until it became a victim of the current climate.
Here, we will use our data to interpret and analyse the skills required to be a success in these leagues and see how many qualities are transferable from league-to-league. Using our unique Batting and Bowling Indexes, we are able to contrast and compare the performances of players from over the course of the respective franchises’ history and see which qualities are, statistically, the most important. As well as the aforementioned tournaments above, we also analyse the last ten years of the T20 Blast in England and the Bangladesh Premier League (BPL) from its inception. Here, we will analyse the different skills needed to be a successful modern-day T20 bowler from league-to-league.
As this article is based around statistical correlations between two variables, the two most important aspects to understand are positive and negative correlation. Put simply, a positive correlation is when one variable increases, so does the other; negative correlation is when one variable increases, the other decreases. The maximum value for a positive correlation is 1 – indicating that as one variable increases the other increases 100% of the time -, whilst the minimum possible value is -1, which would demonstrate that as one value increases the other decreases 100% of the time.
Does more time with the ball in hand bring wickets?
The model we have used to produce our Indexes takes into account not just statistics such as average, strike-rate and economy, but also how each bowler performed on average in comparison to other bowlers in that competition. With many players nowadays dropping in and out of competitions for two, three or four games at a time, we have looked at how consistently players are able to perform over the duration of respective tournaments and rewarded those who have demonstrated success over a longer period.
When looking at the effect of the number of innings’ played on bowling average – the number of runs conceded by a bowler per wicket taken – it is the T20 Blast that has the largest detrimental effect for bowlers in terms of doing damage to their average the more games they bowl in.
For every extra game played in the English tournament, a bowler’s average increases by 0.33 runs, far higher than any of the other competitions, as can be seen below (NB: although the PSL figure appears to be 0, it is actually 0.000388).
Additionally, when looking at the effect of number of innings’ bowled in against bowling strike rate (how many balls bowled per wicket taken), it is again the Blast that has the highest correlative figure at 0.355475, with all competitions seeing an increase when compared against the first graph. However, there are various alterations in the positioning of the tournaments – PSL rising from sixth to fourth; IPL moving from third to second; BPL falling from fourth to sixth – suggesting that the relationship between average and strike-rate is not a linear one. 
Elsewhere, it is interesting to note the effect of innings’ played against a bowler’s economy rate (how many runs conceded per over bowled).
Although five competitions see a drop in economy rate with more innings’ played, the outlier is again the Blast in that economy rates actually rise with the more innings’ played. Whereas in all other tournaments it appears that, the more games played the more economical a bowler gets, the opposite is true in the Blast as it is the only one that shows a positive correlation. The PSL is the one with the most negative figure (-0.2236804), slightly edging out the IPL when it comes to bowlers improving the most with more game time.
As well as time spent bowling, we can also analyse the effect of overs bowled on a bowler’s average because, of course, a bowler may be involved in the innings but not necessarily bowl his whole quota of four overs.
When doing so, a noticeable difference can be seen compared to when analysing against innings’ bowled in as we did previously.
The figure for the T20 Blast remains around the 0.33 mark (dropping a touch to 0.326263), although three leagues drop into a slight negative figure, showing that more balls bowled leads to a lower average, contrasting to what was concluded previously when taking the number of innings’ into account instead.
When looking at overs bowled against wickets taken per innings, the biggest absolute figure is with the T20 Blast, where, surprisingly, for every over bowled bowlers take on average 0.213648 fewer wickets-per-innings, with similarly negative totals for the BBL (-0.115201) and IPL (-0.042759). Conversely, in the CPL, every extra over bowled leads to 0.098748 more wickets, whilst smaller figures are true in the BPL (0.042117) and PSL (0.024338).
This fact is even more extraordinary when considering that the two bowlers with the most wickets in a T20 Blast season over the past ten years are Alfonso Thomas with 33 wickets and Danny Briggs with 31 wickets both in 2010 – but they also bowled the most and third-most overs of anybody in the past ten years with 72.5 and 67 respectively, going completely against the trend displayed by the majority of the data.
Does pressure bring wickets?
Moving on, here we look to see how a bowler’s economy affects the number of wickets he gets. If a bowler is building pressure and conceding fewer runs – gathering a low economy rate – then, with pressure mounting on the batsman and the need to score quickly in T20 cricket, you would expect the batsman to take more risks, play more expansive shots and thereby significantly increase the chances of being dismissed also. This is true in the majority of cases, but with one outlier – as can be seen below.
All leagues bar one have a negative correlation of at least -0.1, meaning that 0.1 wickets are taken for every run saved (so ten runs are needed to be saved in order to gather a wicket). The league with the highest figure is the IPL at -0.255449, meaning that 0.255449 wickets are taken for every run saved. However, it is the Blast yet again that does not follow such a trend, possessing a minimal correlative total of -0.026914, suggesting that fewer runs do not equal wickets.
How important is tight bowling?
Moving on from economy rates, we can also look at the importance of average runs conceded per innings for each bowler to analyse its effect on other variables, too, thus taking into account both their economy and the average amount of balls they bowl.
When comparing the relationship between runs conceded and wickets-per-innings, there is a relatively large spread in the data, albeit with only one competition – the CPL – demonstrating a positive correlation and thus meaning more runs are given away per wicket taken per innings, whilst it is the Blast which has the greatest wicket-taking value per run saved at 0.232811. The four other tournaments also show smaller benefits, with the BBL coming closest to the Blast at 0.135102 wickets per run saved.
What does this mean for the game as a whole?
When combining the statistics from all competitions we are presented with the facts that show us the most important skills for T20 cricket as a whole as a global game. We can judge the qualities that produce the lowest Total Bowling Index (TBI) – the metric by which we are measuring each player’s performance for a given year in a given competition against all other performances in all other competitions. To put it simply, the lower the figure, the more important it is at producing a lower TBI.
It is the number of innings’ played that is the biggest determining factor in TBI with a value of -0.665. The correlative value for wickets taken is -0.609, with runs conceded at -0.561 – showing the value of dismissing batsmen regularly. Elsewhere, the correlative value for average is up at 0.345 compared to figures of 0.306 and 0.241 for economy and strike-rate respectively, suggesting that a harmful average is the factor that has the biggest effect on TBI out of the three. The total correlative heat map is shown below.
Conclusion
Our analysis has highlighted the most important skills for each respective tournament and compared and contrasted how they vary from league-to-league around the world. Want to be a success in the IPL? Make sure you’re there for the whole run. Trying to break into the T20 Blast scene? Wickets are much more significant than runs. Each competition clearly has its own nuances that are required to be a success, as we have analysed here. Stay tuned in the coming days as we analyse the varying skills required to be a proficient batsman in each tournament.
