Cricket has joined some other sports to now have at Test level an umpire referral system. It was first trialed in 2008 (in a Test series between Sri Lanka and India). Unlike in tennis where the challenge and referral decision is clear cut using hawke-eye technology, the cricket referral is adjudicated by another umpire and is open to further errors. The actual way it works may change and develop, but when it was first brought in this is how it worked.
Players are allowed to challenge decisions made by the on-field umpires and have them referred to the TV official. For each innings of the Test, each team can challenge any decisions, though they will be limited to three unsuccessful challenges per innings. Only the batsman on the receiving end of the umpire’s original decision or the captain of the fielding side can appeal by making a “T” sign with both forearms at shoulder height. The third umpire uses the technology of the hot spot and slow motion replays at different angles to gain information and make decisions.
It all sounds great for the players and viewers at home, but the pressure is on the umpires. In reality, the process takes too long and can distract from the game. When there are challenges left near the end of an innings, players tend to make frivolous challenges on the off chance of getting a decision overturned. So there are still problems that need to be ironed out, but a great step forward for cricket.