Wednesday 13 June 2018

How well will Afghanistan's spinners go?

It's a fascinating question - at least two out of 4 spinners who have been very successful in limited over cricket are likely to make their test debut tomorrow. They will be playing in India, a country known for spinning tracks.

The Afghan captain, Ashgar Stanikzai is certainly bullish about their ability: "In my opinion, we have good spinners, better spinners than India."

That's a big call. India have some very high quality spinners in test cricket. But does he have a point?

There is no doubt that Afghanistan's spinners have been good in limited overs cricket, but does that mean anything?

Some spinners have excelled in test cricket and limited overs. Warne, Murali, Shakib, Swann all have excellent stats in all forms of the game.  But others haven't seen such correlation. Amit Mishra, Ish Sodhi, Abdur Razzak and Sunil Narine all have very strong limited overs stats, but have not converted that to test matches.

The comparison of Sodhi and Rashid is an interesting one. When they've played against similar opponents, they have had very similar stats. See for example this graph of combined IPL and Big Bash statistics. (This is the 8 players who played a reasonable number of matches in both tournaments over the past 2 years)

They have clearly been two of the stand out bowlers in the two major domestic T20 tournaments, and yet, Sodhi averages over 40 in test cricket with the ball.

Part of that will be that Sodhi has to play half his cricket in New Zealand, but part of it is also that it is not always possible to predict absolutely test success based on limited over success. They are sometimes linked, but not always.

I wondered if there was a general relationship in the numbers. Were Narine and Sodhi the outliers, or were Warne and Muralitheran the odd ones.

So I tried to construct a model, to see what happened. It turns out, to my surprise, that it is possible to predict, vaguely, the average and strike rate of a bowler in test cricket based on their ODI and T20 performances. I looked at the 37 players who had played as spinners in all 3 formats, had played at least 40 combined limited overs matches and had taken at least one test wicket.

The model is not very reliable, but it was better at predicting the bowling statistics of the players than just taking the average for the group. So it did provide some interesting numbers.

The equations that it came out with were as follows:
Only 4 of the 6 Afghani spinners had played enough limited overs cricket to have meaningful numbers, and here are their predicted results:

That would relate to the following results based on overs bowled:

Those wouldn't be particularly bad returns for a first ever test against India, but they also aren't really the results that Stanikzai is hoping for.

But the question comes up, how reliable is this anyway?

There is a degree of randomness in cricket results that means that any predictions are always quite unreliable. Looking at the graphs of the predicted vs actual for the career stats, it shows that there is quite a bit of variation about the trend.

I've added in the red lines manually, They show where roughly 95% of the data fits. Within 17 of the average and within 20 of the strike rate. Those are huge variations, which shows that it's very difficult to predict test performances based on limited overs performances.

I have added in the best realistic and worst realistic expected figures, based on these confidence bands:

It will be interesting to see which one of these the Afghani spinners actually get closest to.

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