Standards of play across T20 leagues

The world's oldest T20 competition starts again on Friday. The Twenty20 Cup may have been around the longest, but it has since been surpassed by the rest of the world in viewership numbers, attendance, and sponsorship. The ECB have made moves to catch-up, investing a new city-based T20 competition by 2020 but, for now, it is almost certainly true that the T20 Blast also attracts fewer stars than its bigger rivals

I wanted to attempt to quantify the difference in the standard of play between, say, the IPL and the Natwest T20 Blast. I only have one season of ball-by-ball data (2016) and cricket statistics can be highly volatile, so the sample size is small. This seemed like a good opportunity to test whether my Win Probability and Runs Added models could overcome the volatility of traditional stats by accounting for match context when evaluating player performance


 Average first innings total across different T20 competitions. IPL / BBL / T20I / NWB. Natwest T20 Blast is roughly in line with other big T20 leagues

Before delving straight into the ball-by-ball data, I first looked at the average first innings score across different competitions to get a rough idea of the famous balance between bat and ball. The average score in the Natwest T20 Blast 2014-16 is about 165, in line with the IPL (165) and the Big Bash (161).

Scoring in T20Is over the same period is significantly lower but this tells us little, if anything, about the quality of play. It probably doesn't even tell us that international bowlers are relatively more skillful than the batsman counterparts. It is more likely to be caused by the different venues, playing conditions, or a lack of parity between teams

 KC Sangakkara scores more quickly in the Natwest T20 Blast / Twenty20 Cup than in any other domestic league across the world

So let's look at a bowler who has played across a number of T20 competitions and see how he fared against the varying levels of competition. Chris Jordan's economy in the IPL and the Big Bash is 9.23 across (15 matches) suggesting that he finds it more difficult to restrict run-scoring than when playing in his home competition, where he has a 8.58 economy (29 matches)

Then we have Kumar Sangakkara who clear finds it easier to score in the Natwest T20 Blast than in any other competition throughout the world. And he has played in quite a few. We should, of course, be mindful that both Sangakkara and Jordan may be more at home playing in England than in other countries. Sangakkara's extraordinary recent run of consecutive centuries suggests a certain familiarity with English cricket. His second best T20 strike rate is in his home league in Sri Lanka

By finding other players similar to Chris Jordan and Kumar Sangakkara, who have played in multiple leagues, we can create a more robust analysis of the relative competition levels between T20 competitions


(1) Comparing batsmen across leagues on a per-ball basis

The selection criteria when comparing one league against another, was any batsman who has faced at least 50 deliveries in both leagues. For example, there were 30 players who had faced at least 50 balls in the IPL and at least 50 deliveries in the Natwest T20 Blast (NWB). The strike rate of these players was 7.9 points higher in the NWB and they produced 0.09 more Runs Added per ball

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(2) Comparing batsmen across leagues on a per-match basis

The selection criteria was any batsman who played in at least 5 matches in both leagues. For example, there were 22 players who played in at least 5 matches in the IPL and at least 5 matches in the NWB. These players lasted 2.3 balls longer in the NWB and delivered 3.5% additional Wins Produced per match

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(3) Comparing bowlers across leagues on a per-ball basis

The selection criteria was any bowler who bowled at least 50 deliveries in both leagues. There were 27 players who met the criteria for comparing the IPL against the NWB. These bowlers had a slightly better economy in the NWB and restricted opposing batsmen to 0.06 fewer Runs Added per ball


(4) Comparing bowlers across leagues on a per-match basis

The selection criteria was any bowler who played in at least 5 matches in both leagues. There were just 14 players who met the criteria for comparing the IPL against the NWB. On average, it took these players 1.2 balls longer to take a wicket in the NWB than in the IPL. This is the first time that the analysis shows the NWB to be the more difficult of the two leagues. However, this may be situational because these same bowlers increased their team's chances of winning by more in the NWB than in the IPL (+6.5%)


Conclusion

The Natwest T20 Blast emerges as the lowest quality league in each of the four analyses above. By looking at the differences in Runs Added between the NWB and the IPL, we could conclude that an IPL batting line-up would score about 11 runs more per game against an NWB bowling attack, and that an IPL bowling attack would concede about 8 runs fewer per game against an NWB batting line-up

It is also interesting to see that the more traditional cricket statistics align closely to my Wins Produced and Runs Added models for batsmen, but not for bowlers. My hypothesis is that this is because it is easier to control the 'level of difficulty' for a bowler: a fourth-change IPL bowler who is used most during the middle overs may become the top death bowler when they play for their English side. Their economy and strike rate may not improve due to the added level of difficulty but their context-adjusted Win Probability stats should get better

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There is a fairly clear hierarchy between the IPL, BBL and NWB but the results are inconclusive between the IPL and T20 internationals. Head-to-head, batting seems slightly easier in the IPL but bowling seems easier in internationals. If forced to make a call, and without any extra research, I would say that the IPL seems like the toughest level of competition based on its more favourable head-to-heads with the Big Bash and Natwest T20 Blast