The Umpire Decision Review System (abbreviated as UDRS or DRS) is a new technology based system currently being used on an experimental basis in the sport of cricket. The system is being used only in Test Cricket for the sole purpose of reviewing the controversial decisions made by the on field umpires in the case of a batsman being dismissed or not. The new review system was officially launched by International Cricket Council on 24 November 2009 during the first test match between Pakistan and New Zealand at the University Oval in Dunedin.
During a Test match, each team is given two challenges per innings. A fielding team may use the system to dispute a “not out” call and a batting team may do so to dispute an “out” call. The fielding team captain or the batsman being dismissed invokes the challenge by signaling a “T” with the arms. Once the challenge is invoked, acknowledged, and agreed, the Third Umpire reviews the play. While umpires may request the Third Umpire for certain close calls such as line calls (to determine run outs and stumpings) and boundary calls, a challenge may be used in situations that may result in a dismissal: for example, to see if the ball made contact with bat or glove before being caught (making it a legal catch) or to determine if a delivery made or failed the criteria for a leg before wicket dismissal. The Third Umpire then reports to the on-field umpire whether his analysis supports the original call, contradicts the call, or is inconclusive. The on-field umpire then makes the final decision: either re-signaling a call that is standing or revoking a call that is being reversed and then making the corrected signal. If a team’s challenge results in a reversed call, the team keep that challenge; they can continue to challenge throughout the innings until they make two failed challenges.
UDRS (Umpire Decision Review System), the controversial Review System will be used in ICC Cricket World Cup 2011 which is going to be held in subcontinent from February 19th, 2011.