While the DRS was originally introduced to rid cricket of glaring umpiring errors, over the years as teams got the hang of using it, a new dimension has been added to the game. A limit on the number of times reviews can be unsuccessfully used by teams has meant that they have assumed the importance of a resource. Some teams and players are more proficient than others at the use of the DRS and this difference, as shown in the Headingley thriller last year, often turns out to be the deciding factor in contests.
ESPNcricinfo's database says 1141 reviews have been made in Tests since 28 September 2017. That date is when the ICC did away with the rule to reset reviews after the 80th over in Test cricket. This date has been taken as a cutoff for this analysis, to avoid added noise in the data from captains and players making cursory reviews close to the 80th over. Here are a few themes that emerge.
Batsmen know, more often than not
Out of the 1141 reviews called for, 325 have been successful - where the umpire's decision has been overturned. That is one successful review in every 3.5 called for, on an average. Explicably, reviews called for by batsmen have had a higher success rate than those called by fielding captains. As a batsman you are likely to know, more often than not, if you have nicked or haven't, or if the ball is likely to miss the stumps. One in every 2.8 reviews made by batsmen are upheld, as opposed to those by fielding captains, where the success rate is one in 4.5.
Teams are not penalised for reviews that are decided based on the on-field umpire's call as the technology involved doesn't have the confidence to definitively rule out or not out in these cases. It is only fair that such reviews are taken into account when gauging how competent the teams and players have been with their reviewing.
Like with reviews being overturned, batsmen do much better than fielding teams when it comes to retaining reviews. A fraction less than 57% of reviews made by batsmen don't result in the loss of a review (upheld, plus umpire's call). In comparison, fielding teams end up retaining only 36.9% of the reviews they take.
Overall reviews: Pakistan have it figured out
Excluding the two latest entrants to Test cricket and Zimbabwe (these teams have played fewer than ten matches in the period in consideration), Pakistan have been the most successful in overturning umpires' verdict. They have managed to overturn 34.6% (36 out of 104) of reviews. England follow with a success rate of 32.4% (54 out of 176). West Indies are next, at 30.3%. Sri Lanka are the worst in this regard with a review success rate of 23.3%. South Africa (25.4%) and Australia (26.6%) make up the bottom three.
Pakistan lead the lot in retaining reviews too, and are way ahead of any team. They have managed to retain as much as 57.7% of reviews. New Zealand come second with 48.9%. India - who manage to overturn only 27% of their reviews - are placed third, with 48.6% retention. They have been the "unluckiest" of the teams with as many as 21.6% of their reviews struck down on umpire's call.
Fielding reviews: it's Pakistan again
Reviews by fielding teams are often a collective decision and rarely do they involve any personal motivation. On the other hand, reviews by batsmen are often individual-driven. At their inclusive best, batsmen only consult non-strikers before deciding to review. In that sense, fielding reviews offer more of a reflection of how well teams have sussed out the dynamics of reviews.
Pakistan are the most successful team here as well; nearly a third of their reviews are upheld. They are comfortably ahead of England, who have a 24.8% success rate. West Indies follow, on 24.0%. Bangladesh are the worst team in this regard with a review success of just 15.6%, which is less than half the rate of top-placed Pakistan. In terms of retaining their fielding reviews, West Indies lead the pack with a retention rate of 46.0%, followed by Pakistan at 43.1%. Sri Lanka and South Africa are the unluckiest of the lot, as 58.1% and 52%, respectively, of their reviews that could have gone either way go against them.
Sri Lanka have it muddled up
Sri Lanka's batsmen take 55.86% of potential reviews (which is a total of minimum reviews of two per innings plus reviews retained through umpire's calls and review overturns) available to them - which is more than any other team. They average 1.56 batsman reviews per innings - the highest of any team. India are second with an average of 1.43 reviews per innings.
But while all other teams are top-heavy in their reviewing pattern - batsmen in the top six account for a higher portion of reviews than those in the bottom five - Sri Lanka are the only team whose last five batting positions account for nearly 60% of their reviews.
This suggests that their top-order batsmen are review-shy and are perhaps not calling for reviews when they should, and are leaving reviews unused for their lower-order batsmen, who take them because they are available anyway, and spoil the team's overall review success rate.
Dilruwan Perera, the Sri Lanka offspinner, has taken more reviews, 17, than any other Sri Lanka batsman, batting largely at No. 7 or 8 (in fact, he has taken more reviews than any other batsman from any other team during this period). In comparison, Sri Lanka's batsmen from No. 3 to No. 6 have a combined tally of just 14 reviews. Dimuth Karunaratne is their only top-order batsman in the top five of their most frequent reviewers. Suranga Lakmal (eight reviews), Niroshan Dickwella (seven, batting at No. 7 or No. 8) and Rangana Herath (five) complete their top-five reviewers.
Admittedly, their top-order batsmen may not have been in situations to take reviews, but the evidence from available data is intriguing.
Kohli drives India's top-order excess
India on the other hand, follow almost to a fault the guideline that the best batsmen should get the most chances. Batsmen in their top six have used 72.3% of their reviews - more than any other team's. Kohli leads the pack with 12 reviews of his own, which accounts for 18.5% of the reviews all of India's batsmen have made. Only one of them has been successful. His success rate of 8.3% is the worst among the 34 batsmen with five or more reviews - barring Usman Khawaja, who has not managed to overturn any of his five reviews.
India's top six have been successful only 29.8% of the times they have gone upstairs. No team has done worse. They manage to retain only 55.3% of their reviews for their team; only West Indies have done worse on that count.
Nice guys shirk challenging authority
New Zealand use up only 47.57% of their reviews. No other team is as conservative. Apart from them, Bangladesh are the only team to not use at least 50% of their available reviews. Admittedly, teams may not get opportunities to make use of all the reviews that are potentially available to them in each innings, but that is true for all teams. And New Zealand are equally conservative with both their batting and fielding reviews. They are the only team to not use at least 50% of their reviews in both disciplines.
Root, England batsmen set reviewing benchmark
Joe Root's experience with the DRS - he has presided over more DRS calls than any other player since October 2017 - shows in his review of decisions against him while batting. Seven of his ten reviews have been upheld - a success rate of 70%. Hashim Amla is the only other batsman with more than five reviews to have a higher rate of success than Root. Amla has got a verdict in his favour five out of the six times he has gone upstairs.
England's top six review better than any other team: they have successfully overturned 48% of decisions against them. They are only behind Pakistan in terms of retaining reviews for their team, with a rate of 68%.
Captains, heed Messrs. Abbas and Woakes
Pakistan have been successful at overturning seven out of the 15 (46.7%) on-field calls off the bowling of Mohammad Abbas. No other bowler with at least 15 reviews taken off his bowling has a better success rate. Chris Woakes has done better for England. In five of ten reviews off his bowling, the on-field umpire's decision has been overturned.
Teams also retain at least half their reviews made off the bowling of these two bowlers. Captains had better pay attention when these guys insist on taking a review. A wicket might just be around the corner.
With inputs from S Rajesh