DRS: The story so far

As the internet matures, the amount of freely available data has reduced. So I was excited when this popped up on twitter:

A chance to examine some of the received wisdom on the review system. I’ve got five myths and three trends to share with you.

Before we get into that, a summary. Over the decade of Decision Reviews, most reviews have been by the fielding team (57%). However, batsmen have had greater success overturning dismissals (35%, compared to 21% for the fielding team). The 907 overturned decisions are 6% of the wickets over the last decade, so while umpires are getting the overwhelming majority of decisions right, DRS is making a noticable difference to the accuracy of umpiring.

On with the show. Firstly, five myths:

I’m going to have to ask you to reverse your opinions

Myth 1 – Umpires favour the home team

Crunching the numbers, the hosts and visitors have uncovered almost exactly the same number of incorrect and borderline decisions. In terms of overturned decisions it’s 416-413 in favour of the home team, while the marginal decisions that haven’t been overturned (“Umpire’s Call”) have benefitted the home team slightly, with 109 reviews by the visitors being adjusted Umpire’s Call, against 100 for the home team.

If umpires were being influenced by the crowd, there would be more decisions against the away team then being overturned – this isn’t happening, so whatever home advantage is in Cricket, it’s not from umpires.

Myth 2 – Having a decision overturned gets into an umpire’s head

I took each example of an umpire who had a decision overturned, and looked at the next DRS review for that umpire on the same day in the same innings. If umpires were trying (even subconsciously) to even things up, you’d expect the umpire to give the next close one out, which the batsman would review. Putting this in terms of data, we’d look for a decision overturned against team A to be followed by a review by team B.

No evidence for this exists – of the 449 times when a decision was overturned and another review occurred on the same day, same innings, same umpire, 235 were the other side reviewing, 214 the same side. Umpires are considering each ball on its merits.

Myth 3 – Teams use reviews “just for the sake of it”

This one really surprised me. I’d expected to need to cleanse the data of the pointless reviews at the end of an innings when there’s no harm in reviewing. So I looked for those pointless reviews, but they don’t exist.

Opportunistic reviews should be visible by a dire success rate. Here’s the split of success rate by the batsman’s average:

Maybe a handful of spurious reviews from the worst batsmen, but they aren’t taking the mickey.

Myth 4 – Some teams are better at DRS than others

Not true – all the teams are very tightly bunched. I’ve excluded Afghanistan (30%), Ireland (50%) and Zimbabwe (30%) as they just haven’t played enough.

Myth 5 – Some umpires like to give things out and some like to say “not out”

There are two ways this would manifest itself for Outers: “Umpire’s Call” would tend to be batsmen reviewing balls, clipping the stumps, that were given out; and the proportion of successful reviews would be higher for batsmen.

Because of the small sample sizes, it looks like there are trends, but when you put the two methodologies side by side, the pattern disappears. Which is a shame, because I’d hoped that the umpires who were bowlers would be Outers and those that were batsmen would be Not Outers. Turns out Elite Umpires are just professionals. Here’s the chart for good measure.

Now for the true trends

Stay with your original opinions; you’re on screen now.

Trend 1 – Quality of reviews drops by day

Tony Corke (@matterofstats) got in before me with this trend – here’s the chart he produced

Trend 2 – Resetting reviews after 80 overs (2013-17 rules) reduced review effectiveness

The long term trend is fairly consistent – flitting around the 27% mark. Except for 2014 and 2015. I think I can explain that dip.

In 2013 a rule was brought in whereby reviews reset after 80 overs. This was to avoid punishing a team who lost reviews to marginal decisions. A better rule took over from autumn 2017 – “Umpire’s Call” decisions would not cost a review.

The impact of the resetting reviews was felt in overs 60-80: teams were in a position of “use it or lose it”, so did the logical thing and reviewed liberally. Thus, from 2013-16 the success rate in overs 60-80 was only 20%, having been 28% for those overs before 2013. Naturally, once the new rules took over from 2017, the success rate for overs 60-80 returned to 28%.

Trend 3 – DRS success rates differ by ground

The harder batting conditions are, the better the relative performance of fielding reviews versus batting reviews. Any scatter plot for this looks ugly, so you’ll just have to take my word for it that this is a statistically significant correlation. In lieu of that, here’s a chart of batting and bowling DRS success rates by ground.

Now, I’m not sure which way the causation runs. One possibility is that at high scoring grounds the umpires get lulled into thinking batsmen aren’t going to get out, so they don’t believe their eyes when a batsman is out.

The key point I’d like you to take from this is just how consistent umpires are.

Off spinners, DRS, Left Handers, and a new way of looking at averages

How can you tell if a bowler is better than average? They cause batsmen to underperform.

Muttiah Muralitharan troubled batsmen to the extent they averaged eight runs per wicket fewer than over their careers. Mark Boucher averaged a paltry 21 against Murali, whilst his career average was 30.

So what? Well, dear reader, the title of the piece gives you a clue where this is going.


DRS was first used in a Test match in 2008, and subsequently rolled out at the back end of 2009. This led to an increase in LBWs for spinners as the technology changed perceptions of how often spinners were delivering balls that would hit the stumps.

Fig 1 – percentage of bowled and LBW for leading off spinners this century (excludes Jeetan Patel, who evenly spanned both decades).

The chart shows a notable increase in the proportion of bowled and LBW dismissals for spinners in the 2010s.

Fig 1 indicates that off spinners only got a little benefit from DRS. This makes sense: coming over the wicket they can’t bowl too straight as that opens up run scoring opportunities. Turning the ball in to the right hander from outside off gives the batsman an escape route (by ensuring contact with the pad is outside the line of the stumps).

Now look at the left handers. A revolution. Instead of 30% of wickets coming from bowled/LBW, that rocketed to 45%. A simple post-DRS approach for an off spinner is to come round the wicket to a left hander and pitch on off stump. Any big turn catches the edge; while no turn means bowled/LBW are in play. Pre-DRS left handers had the opportunity to get a good stride in and using the pad as first line of defence. That doesn’t work with ball tracking. The camera knows.


UPDATE 31st JAN 2020 – In the below table, columns “RHB impact” and “LHB impact” were based on potentially inaccurate data. I need to do more work to prove this – so please don’t rely on it for now.

Fig 2

Fig 2 is a ruddy goldmine. Let’s break it down.

  • First two columns: the player and the decade they mainly played in
  • Third column: career average
  • Fourth column: impact on the averages of the batsmen they bowled to. The better the bowler, the lower this number would be. For an average Test cricketer this number would be nil. Calculated by comparing (runs conceded against each batsman) to expected runs conceded (wickets taken * batsman’s average).
  • Fifth to seventh columns split the Bowler Impact metric between right and left handed batsmen

In the 2000s, left handers were the batsmen of choice to counter a strong off spinner. Only thee batsmen averaged more than 52 against Muralitharan – all were left handers*. A left hander against Murali could expect to average three runs more than his right handed equivalent.

However, that benefit reversed last decade. The hunter has become the hunted. Swann and Ashwin didn’t adversely affect right handers’ averages, but lopped five runs per innings from left handers.

That point is really interesting, so I’ll say it again another way. It’s wrong to see Graeme Swann as a very good Test bowler against everyone – he was average against right handers yet brilliant against lefties. That averages out to “very good”.


  • A bowler’s ability can be represented by their impact on a batsman’s average, as an alternative metric to bowling average.
  • Off spinners represent a clear and present danger to left handers.
  • The general case for matchups in Tests: RHB +8%, LHB -13% vs Off Spin. RHB -7%, LHB +14% vs Leg Spin.
  • Previously I’d adjusted a batsman’s expected average to reflect the bowling attack’s averages. Will need to add to that the type of bowler and whether the batsman is left or right handed.
  • I’m working on the basis that all off spinners are alike – explicitly assuming relative performances of right/left handers against a particular bowler are the result of low sample sizes.
  • Will look at left arm pace and slow left arm bowlers next.

*Qualification criteria: dismissed four or more times

Further reading

Ricky Ponting argued for Australia to favour right handers in the 2019 Ashes to nullify the threat of Moeen Ali.