Game on: Rudi Koertzen signals the first-ever Powerplay during the match between Australia and England at Headingley in June 2005 © Getty Images

What is a Powerplay?
The 15-over field-restrictions rule - under which a fielding side could have only two fielders outside the 30-yard circle, and needed to have two fielders (apart from the wicketkeeper) in close catching positions - in ODI cricket was replaced in June 2005 by Powerplays, under which there are three sets of field restrictions of ten, five, and five overs respectively.

An umpire signals a Powerplay by making a circular motion of his arm.

How are Powerplays different?
Previously, all 15 overs of field restrictions were necessarily played out at a stretch at the start of an innings. Under the Powerplay rule, only the first set of Powerplay overs needs to occur at the beginning of the innings. The other two sets are available to the fielding captain at any time during the innings, but must be used in the course of the 50 overs.

During the second and third Powerplays it is not compulsory to have two men in close catching positions, unlike in the first Powerplay or as under the earlier rules.

The fielding side can choose to have three fielders outside the circle in either the second or third Powerplay. The fielding captain has to advise the umpires as to which of the blocks of Powerplays he is using to have three fielders outside the circle during. The umpire signals that Powerplay in the normal manner, but follows it by a hand signal with three fingers extended.

What inspired the rule change?
The one-day game was growing increasingly predictable, with batsmen preferring to attack in the first 15 overs of field restrictions, and in the death overs, rendering the middle overs eventless. The Powerplay rule was designed to keep up the excitement all through a 50-over innings.

How are the Powerplay spells determined in a curtailed match?
The total number of restriction overs is the closest whole number to 40 per cent of the total number of overs in the innings. Whatever the revised number of overs is, the first ten are considered Powerplay 1. For example, in a 41-over game, the total number of Powerplay overs will be 16, and the Powerplay spells will be 10, 5, and 1.

How do Powerplays work in Twenty20 matches?
The calculation of restriction overs works as in an old-style ODI. In an uncurtailed Twenty20 match, the number of restriction overs is six, and these are played at a stretch at the start of the innings, while in curtailed matches it is the closest whole number to 30 per cent of the total number of overs in the innings.