Here’s an explanation of how the Decision Review System (DRS) worked in the case of the leg-before appeal against Ian Bell on 27 February in the game between India and England at Bengaluru.
* The greater the distance between point of impact and the stumps and the shorter the distance between point of pitching and the point of impact, the more difficult it is for the technology to provide an accurate projection.
* For this reason the playing conditions provide that in the case of a not out lbw decision where the distance between point of impact and the stumps is greater than 250 cm and/or the distance between point of pitching and point of impact with the pad is less than 40cm (as will be indicated in the Hawkeye graphics and with the attached being an example), the umpires are not obliged to follow the normal rules for using Hawkeye to determine whether the batsman is out or not and shall have a discretion in determining whether or not to overturn their original not out decision.
* In exercising this discretion they are required, in consultation with the third umpire, to take into account normal cricketing principles for determining lbw decisions.
What are these normal cricket principles?
These are a combination of factors:
* The distance between point of pitching and point of impact (the shorter this distance, the more difficult it is to be certain that the ball will go onto hit the stumps and thus the more unlikely it will be that the umpire will change his not out decision).
* The distance from point of impact to the stumps (the greater this distance, the more unlikely it will be that the umpire will change his decision)
* Where the ball is predicted to hit the stumps (the further this point from the centre of middle stump, the more unlikely it will be that the umpire will change his decision).
But it is a combination of the above factors that must be taken into account by the umpire in consultation with the third umpire.
E.g. If the batsman double steps and gets hit on the pad 4 metre down the wicket, the umpire will not change his not out decision even if the ball is predicted to be hitting the middle of middle stump, especially if there was only a short distance between the points of pitching and impact on the pad.
There have been two instances in ICC Cricket World Cup 2011 where a not out leg-before decision has been reviewed by the fielding side where the point of impact was more than 2.5 metres from the stumps. In both these cases:
* the distance from point of pitching to point of impact was approximately the same
* the distance between point of impact and the stumps was just over 2.5 metres
* The ball was predicted to hit the stumps slap bang between off and middle stump about 3/4 of the way up.