In the second edition of the IPL, played in 2009 in South Africa, Royal Challengers Bangalore consistently played five Karnataka players in their eleven, which meant that these players frequently spoke to each other in Kannada. Back then it wasn’t common to find Karnataka players playing for other teams in the IPL, and so speaking in Kannada was one way for RCB to talk “in secret”.
One of the defining images of that IPL was Robin Uthappa, keeping wicket for RCB, shouting “kaal muri” when Anil Kumble was bowling. Kaal muri literally translates into “leg break”, and Uthappa was essentially asking Kumble to bowl what is not his stock ball (if you remember right, Kumble used to mostly bowl flippers and googlies, and not turn the ball much).
As it happened, 2009 also represented the trough of leg spin in ODI cricket. Going by cricinfo ball by ball data, only 4% of overs in that year were sent down by leg spin and chinaman bowlers. It stayed around that range until 2013, but since then we’ve seen a remarkable rise of leg spin bowling. In the 66 ODIs played in 2019 so far, nearly 15% of the overs have been bowled by leg spinners!

Going into the World Cup, all major contenders have one or two prominent leg-spinners in their ranks. India has Yuzvendra Chahal and Kuldeep Yadav. Australia has Adam Zampa. England has Adil Rashid. South Africa has Imran Tahir. Yasir Shah’s persistent injuries mean that Pakistan goes in with Shadab Khan as their main leg-spinner. And while he doesn’t play for a “major team”, we can’t count out Afghanistan’s Rashid Khan.
Most of these spinners came into the side in the 2013-15 period. Adil Rashid was included by England in their post 2015-debacle overhaul and he’s remained a fixture since then. India flirted with Amit Mishra in the 2013-15 period, but after the 2017 champions trophy loss, have stuck to the duo of Chahal and Kuldeep. Yasir Shah came into Pakistan’s side as the second leg-spinner for the 2015 World Cup (along with Shahid Afridi), but injuries have meant that he’s lost his place to Shadab Khan, who is also an adequate batsman.
I have a few hypotheses about why we are seeing so much leg-spin in ODIs nowadays. Firstly, the use of two new balls since late 2011 has meant the need for bowlers who can bowl consistently well with a relatively new ball. And with their preference for the hard ball, leg-spinners slot in naturally.
Then, the rise of leg spin can also be attributed to the high-scoring 2015 World Cup. As games have become more and more high-scoring, teams have been looking for bowlers who can take wickets rather than contain and leg-spinners fit in there as well.
And then you have positive feedback - as leg-spinners have done well in ODI cricket, teams have tried to play more leg-spinners. For example, West Indies brought in Test specialist Devendra Bishoo into their ODI side (though he’s not gone to the World Cup). (that said, I must point out that under normal cricketing metrics such as strike rate, economy rate or bowling average, leg spinners haven’t exactly been superior to other kinds of bowlers in this time period).
Finally, the decline of leg-spin through the latter half of the 2000s - when Shane Warne and Anil Kumble had retired, and Afridi was a sort of lone flagbearer for leg spin bowling - meant that batsmen had sort of forgotten how to play quality leg spin. We saw evidence of this in the recent IPL as well, as batsmen of the caliber of Virat Kohli and AB de Villiers struggled against the likes of Shreyas Gopal.
And whatever the reasons that leg-spinners are playing more, the way teams are using them has also changed. Earlier, leg-spinners used to be the stock bowlers for middle overs, bowling most of their overs between overs 21 and 35. As leg spinners have gained prominence, teams have started using them outside this window as well.
Leg-spin is still absent in the first ten overs and last five overs of the innings, but it is increasingly common to see leg-spinners bowl in overs 11-20 and then until over 45. Again it is possible that their ability to handle the hard ball means they can come in earlier (finger spinners prefer an older ball).

With the pitches in England reputed to be flat, it is expected that leg-spin will play an important role in the tournament. We doubtless have several quality leg-spinners going into the tournament, but it will be interesting to see if batsmen have a different plan of attacking them.