What is Decision Review System in cricket and how does it work?

Referral system has reduced the number of umpiring errors

England batsman Joe Root asks for the third umpire's review after being given out against India in the first Test in Hyderabad. AP

Cricket is one of the most enthralling sports in the world, but even its most ardent fans will admit it can get very complicated.

There are more than a dozen field positions, 11 modes of dismissals, different formats, varying duration of matches, field restrictions, and so on.

A newcomer might take months to cover the basics of the game, and a lot longer to grasp the intricacies of it.

The complexity was one of the reasons why cricket did not develop outside its traditional Commonwealth bases, but which is also one of its more charming aspects.

And you can’t get more complicated than the decision review system, which was introduced to reduce umpire errors.

As TV technology became more advanced at the turn of the century, umpire errors and their impact on match results got magnified to a degree where the same technology had to be utilised to reduce ‘human error’.

And thus, in 2008, the Decision Review System (DRS) – where players could directly review an umpire’s call – was trialled for the first time during a Test series between Sri Lanka and India.

From there, after a long-drawn process, the player DRS has become an integral part of international cricket with standard rules and implementation.

There are two types of reviews – one called by the umpires and the other requested by the player. There are no restriction on the number of times that on-field umpires can consult with the third umpire on calls and decisions. However players are restricted to a set number of unsuccessful challenges; and that is what we are looking into.

What is the Decision Review System?

It is a system by which players – either the fielding side or batsmen at the crease – can challenge a decision made by the umpire, whether out or not out.

Once a dismissal or non-dismissal has been adjudged by the umpire, the players have 15 seconds to consult among themselves to challenge the call by making a ‘T’ sign with their hands.

If the fielding side wants to challenge the decision, the call has to be made by the captain.

In Tests, teams are allowed three unsuccessful reviews per innings. In ODIs and T20s, it is two per innings.

What decisions are referred by players?

Two modes of dismissals – caught behind and lbw – are mainly referred by the players.

These are the modes of dismissal that generally require multiple technology, replays and angles to arrive at a decision, unlike other dismissals such as run out or catches in the outfield, which can be adjudged by a simple replay and are called by the umpire themselves.

Out of the two, the leg before wicket is the most laborious. First, the umpires check whether the batsman hit the ball or not. Then, whether the ball pitched outside the leg stump. Thereafter, whether the impact of the ball hitting the pads was outside the line of the stumps. And finally, whether the projected path of the ball would hit the stumps flush or partially or miss altogether.

Depending on whether the umpire originally gave the player out or not out, the subsequent findings upon player review assist the final verdict of the third umpire.

What technology is used for DRS?

There are three main tools used by the third umpire to adjudicate referrals. Apart from slow motion replays, the main technologies used are:

1. Hot spot: Thermal imaging used to detect whether the ball has touched the bat. Since it requires infrared cameras and does not always provide conclusive angles when ball goes past the bat, it is not widely used now.

2. Ultra Edge / Snicko: This is highly tuned audio device that picks up the faintest of edges, which works in conjunction with real time footage to show whether the batsman has edged the ball. In most cases, it shows a clear spike when the ball even brushes the bat’s edge.

3. Hawkeye: A highly sophisticated technology that was developed for cricket to aid lbw decisions, Hawkeye has been further refined and used extensively in sports like tennis and football. It is a ball-tracking technology that predicts, with accuracy, the projected path of the ball.

Hawkeye, which uses multiple camera angles, is mainly used to check whether the ball would have hit the stumps during lbw reviews, after taking into account the speed, bounce, and trajectory of the ball.

When does a decision get overturned?

Generally, especially with lbw referrals, there is enough evidence for the third umpire to adjudicate one way or the other.

Technology for detecting whether the batsman hit the ball and where the ball pitched are advanced enough to make it a clear-cut call – whether to uphold the decision made by on-field umpire or overturn.

But ball-tacking, which is the last step of the referral process, gets a bit tricky as it is a projection, after all. In the case of lbw calls, if the ball is projected to just brush the stumps, the final decision goes back to whatever the on-field call was – out or not out.

What has been the impact of DRS in cricket?

The number of bad calls has definitely come down in cricket; players who are clearly out or not out are readily found out.

There is a feeling among experts that umpires nowadays are more willing to give lbw decisions, knowing that technology is available to aid them in case they make a mistake.

However, according to data collected by ESPNcricinfo over the past two decades, there is almost no change in the actual number of lbw dismissals. In the decade before DRS was introduced (in 2008) and in the subsequent years after it, the percentage of lbw in all dismissals in international matches has been around the 17 per cent mark, be it partial or universal DRS implementation.

The percentages have remained almost exactly the same, which makes sense since international standard batsmen would normally miss roughly the same number of balls over a period of time and across various pitch conditions.

What has changed, however, is the number of bad decisions in those 17 odd per cent lbw decision. YouTube videos of old matches are filled with horrible umpire decisions, which have thankfully come down to close to zero with DRS involved.