What analysts of T20 cricket can learn from basketball
Welcome to the first edition of Plot the Ball for 2023.
Rather than a single post at the end of each month, this year — while I work on a number of other related projects — the newsletter will be less formal and won’t follow as regular a pattern.
You will still be able to find the (uncommented) code I've written to perform these analyses on GitHub.
What analysts of T20 cricket can learn from basketball
The fundamental premise of the analytical revolution in basketball is often expressed in mathematical terms: 3 > 21.
In plain English, the key insight is that three-point field goal attempts are simply worth more than two-point field goal attempts2. Team’s attacking strategies have been altered accordingly, and the sport’s record-keeping has also been updated in order to reflect these relative values.
Analysis of shooting performance in the modern version of the sport now tends to avoid simple ‘field goal percentage’ (FG%) — successful attempts of any value as a proportion of all attempts — in favour of ‘effective field goal percentage’ (eFG%). Per Basketball Reference:
“[T]he formula is (FG + 0.5 3P) / FGA. This statistic adjusts for the fact that a 3-point field goal is worth one more point than a 2-point field goal. For example, suppose Player A goes 4 for 10 with 2 threes, while Player B goes 5 for 10 with 0 threes. Each player would have 10 points from field goals, and thus would have the same effective field goal percentage (50%).”
It may not be immediately obvious, but there’s a lesson for cricket in all of this.
As the Twenty20 format continues its slow takeover of the entire calendar, ‘boundary percentage’ — defined as the proportion of balls faced hit for a boundary four or a boundary six3 — is embedding itself in the sport's lexicon4.
But as a metric it suffers from the same problem as FG% in basketball: treating all shots equally, even though one of the two sub-groups is worth 1.5x the other.
In the same way that using eFG% is a more accurate way of analysing a player’s shooting performance in basketball, calculating and tracking ‘effective boundary percentage’ would be a further step towards capturing the true value of batting performance in short-format cricket.
Boundary %: (Boundary 4s + Boundary 6s) / Balls Faced
Effective Boundary %: (Boundary 4s + 1.5 * Boundary 6s) / Balls Faced
To put this in more concrete terms, consider South African starlet Dewald Brevis. The all-rounder will represent MI Cape Town in the inaugural edition of the SA20 franchise tournament which starts in his native country later today.
Even at age 19, his attacking intent with the bat has already made him a sought-after player in major T20 leagues across the world.
In his cameos in the Indian Premier League and Caribbean Premier League last year, he was clearly an above-average batter even by simple boundary percentage: he hit 22% of the balls he faced in the former competition either for four or for six, and 20% in the latter5.
But — given his ability to completely clear the boundary with unusual frequency — the metric doesn’t give his performances all of the credit they deserve.
In the CPL, for example, he hit 16 boundaries in 81 balls — but 13 of those boundaries were sixes.
Using the formula laid out above, this works out at an effective boundary percentage of 28%.
DEWALD BREVIS: CPL 2022
Boundary %: 16 / 81 = 20%
Effective boundary %: (3 + 1.5 * 13) / 81 = 22.5 / 81 = 28%
Brevis jumps all the way up to rank 4th by this metric among batters in the 2022 CPL; in the 2022 IPL6, he moves up to to 10th with an effective boundary percentage of 27%.
In essence, assessing batters’ ‘boundary-hitting’ skills in the abstract is not precise enough — as not all boundaries are of equal value.
It’s also worth noting that — as well as giving additional credit to players who are undervalued by more traditional measures — such analysis will highlight batters whose boundaries are disproportionately more likely to be fours than sixes (and hence who are overvalued by simple boundary percentage).
Jonny Bairstow’s performance in last year’s IPL7 is an example of this: he ranked 7th among batters with more than 60 balls faced by simple boundary percentage (25%), but dropped to 9th when the same players were ranked by effective boundary percentage (27%).
Returning to Brevis specifically: while his major-tournament experience is still limited8, his hugely impactful performance in Cricket South Africa’s domestic T20 competition prior to Christmas is further evidence that his ability in this regard is likely to be exceptional9.
And, if you’re planning on tuning into any SA20 matches over the coming weeks, he’s also simply a really fun cricketer to watch.
The right-hander hews almost perfectly to the archetype for top-order white-ball batters former England selector Ed Smith recently laid out in an interview with ESPNCricinfo:
“They have that ability to hit good balls through the off-side field, playing relatively low-risk shots - and the fielding restrictions mean there are always gaps on the off side in the first six overs - and then when there's a mismatch, they have the potential to hit 22 or 24 runs off an over, playing higher-risk shots, often to the on side."
There are many examples of leg-side power-hitting in Brevis’ CPL highlight reel, and his impressive performances in the 50-over U19 World Cup in early 2022 contained plenty of more controlled boundaries through the off-side.
The South African is a very modern cricketer — and it takes a more progressive approach to analysis to fully appreciate his batting skillset.
You can find the code for this piece on GitHub here
More accurately: 3 multiplied by the probability of an average three-point field goal being successful > 2 multiplied by the probability of an average two-point field goal being successful.
Even after adjusting for the fact that the success probability of an average two-point field goal is higher than that of an average three-point field goal.
Rather confusingly, further in the past it seems to have also been used to refer to the proportion of a batter’s runs which were scored in boundaries; at ESPNCricinfo at least — which is about as canonical as it gets — that usage has since fallen by the wayside.
The IPL average for 2022 was 18%; the CPL average was 16%.
He hit 14 boundary fours and 11 boundary sixes.
Bairstow hit 34 boundary fours and 9 boundary sixes.
He faced only 194 balls combined across the IPL and CPL in 2022.
He had the highest effective boundary percentage among CSA T20 Challenge batters at 32%.