Because India continues to oppose it, questioning the effectiveness of the technology involved, and because it leads to decisions that remain controversial. India's opposition has prevented its use in bilateral cricketing series involving India, though it is mandatory in ICC events. Two of its strongest backers, Australia and England, have now suffered a number of DRS howlers in the ongoing Ashes, which has ignited the debate afresh.
How does DRS work?
A cricketing team not satisfied with the umpire's decision calls for a review by a TV umpire, the number of reviews limited to two per innings. The technology includes Hawk Eye that projects the trajectory of a delivery, Hot Spot that determines if the ball has touched the bat, and stump microphones to detect small sounds of the ball hitting the bat.
Is it effective?
Hawk-Eye and Hot Spot have a success rate not more than 95 per cent, as admitted by the companies that developed the systems. Also, Hot Spot can be deceived by applying certain chemicals to the bat, and bat-tampering allegations have indeed come up in the Ashes. To be 100 per cent correct, cameras need to by placed at the level of the umpires' eyes, which is not possible. Ball tracking is based on conjecture and interpretation.
What has happened now?
Usman Khawaja and Kevin Pietersen in the third Ashes Test, and Ashton Agar in the second, were given out based on audio evidence though Hot Spot had shown nothing. In the first Test, Trott was given lbw though side-on Hot Spot was not available; the cameras cannot cover all angles. Steve Smith and David Warner too have been DRS victims.
How have the teams taken it?
The International Cricket Council has had to rush an official, director of cricket operations Geoff Allardice, ahead of the fourth Test. He will meet England team director Andy Flower and his Australian counterpart Darren Lehmann. Even former England captain Michael Atherton has been demanding the removal of Hot Spot from DRS, saying it is creating more confusion rather than solving the riddle.
What is India's current position?
The same as ever. The BCCI's interim head, Jagmohan Dalmiya, has said he doesn't see "any chance for DRS in its present form" and reiterated that India would accept it only when the technology is foolproof. The BCCI's president-in-exile N Srinivasan is against players questioning the field umpires' authority.
Has India ever tried it?
They suffered when it was first used, in 2008. After a tour of Sri Lanka, almost all Indian players expressed their unhappiness with BCCI officials. The BCCI in turn asked for demos from Hawk-Eye and Hot Spot. Unconvinced, they summarily rejected the system.