The Effective DRS

              The hawk-eye was first used in 2001 and it took seven more years to use the same technology to correct umpiring errors. There has been a lot said about the faults in the current system. The Indians, after losing multiple reviews due to poor reviews in Sri Lanka started questioning the system itself and haven't used it in a bilateral series,since then. But, the system is still doing an efficient job in correcting major umpiring errors. Thus, serving its purpose. 

             Most predictions that the hawk-eye comes up with seem to be fairly believable. There could be minor alterations in the predicted trajectory of the ball, but it would still be better than the trajectory predicted by the umpire which is why there seems to be very less logic in what the Indians have to say. Coming to Hot Spot, it picks up all edges that a human ear can pick up and a few edges that the human ear can't which means it corrects major umpiring errors and hence, serves the purpose. 

               With the main purpose of the DRS being that major umpiring errors (or to refer to the commonly used term "howlers") be corrected, one of the main problems with the current system seems to be management of the number of reviews for a side. For instance, if a team uses up their reviews on two close calls and then a howler is committed, the current system fails to serve the intention with which it was brought in. It is now in a binary format where reviews are lost if the decision is upheld and retained if reverted, which if altered would help teams in retaining their reviews with close calls and hence would eliminate howlers if committed at a later point in an innings. 

The alteration has to be done differently for each situation as summarized below

Reveiwing a Catch

              A catch only has two components, prediction of an edge and whether the catch was taken cleanly by the fielder. Deciding what a close-call is pretty hard. The thing that could be done is, if a catch is referred and the replays are unclear that there was an edge or the catch was taken cleanly, the review should be retained by the reviewing team. This holds true in cases where either the batting or the bowling side has made a referral.

Reviewing an LBW when the Batsman hasn't offered a shot.

             When the batsman hasn't offered a shot, the only component that is going to matter is how much of the ball was hitting the stumps which means that there could be 2 scenarios.

1. Batting side has reviewed the LBW
• In this case, if less than 40% of the ball is hitting the stumps, the batting team should retain the review.
2. Bowling side has reviewed the LBW
• In this case, if more than 60% of the ball is hitting the stumps, the bowling team should retain the review.

An LBW is reviewed when the Batsman has offered a shot

          This scenario is a little complicated considering that there are different parameters which will decide the final decision. For each review that is made, the reviewing team gets points based on the positioning of the ball and prediction of the edge. If the number of points acquired for the referral goes beyond a certain threshold, the team that has reviewed the decision gets to retain the review. The points system will vary based on whether the batting or the bowling side reviews the decision.

Points System when Bowling Side Reviews an LBW

The points system has two parts to it

Ball Positioning

          The prediction of the position when the batsman has offered a shot has to happen with respect to 3 categories. The difficulty in predicting the position of a ball would increase in the following order

1. Pitching outside Leg Stump
2. Point of impact with the Stumps
3. Point of Impact with Batsman's Leg.

Hence, weights have been assigned appropriately for each of these categories. Points for each category will be obtained by multiplying with the weights. Finally, the points acquired by the team in prediction of position of a ball will be sum of all points acquired in each category.

Points System when the Batting Side Reviews an LBW

Edge Prediction

             With edges, different situations come up with the 2 categories shown. The table depicts 12 scenarios and depending on the scenario that the referral is made will decide the points acquired for edge prediction. The sum of all points acquired with respect to ball positioning and edge prediction should be greater than a certain threshold for the team to retain the review. Hence, deciding on a suitable threshold will become a very important aspect to this system. 

Frequency of possible Outcomes

             Different combinations of ball positioning and edge predictions will lead to different outcomes (in terms of points acquired by a team). A detailed understanding of what the possible outcomes are and the frequency of their occurrence will help deciding the threshold for retaining a review. The possible outcomes and their frequencies are depicted in the image shown. This shows that a total of 7290 outcomes are possible. Out of those about 60% of the outcomes starting from 0 should mean that the team will not retain the review and the other way round in case of the remaining 40%. This would give us a threshold of 150, which means any team that gets points equal to or more than 150 would retain their review. With this threshold set, on 2746 occasions out of the 7290, the team reviewing will get to retain their reviews, thus will help solve the problem of correcting howlers committed in an innings even though reviews on close-calls were lost by the reviewing team, making the DRS "The Effective DRS".

One important point to note in all these conditions is that the decision making with the current DRS will still remain the same, the only change would be that the team reviewing would get to retain reviews in case of close calls.