In the main the Laws of cricket apply. However, in ODIs, each team bats for a fixed number of overs. In the early days of ODI cricket, the number of overs was generally 60 overs per side, and matches were also played with 40, 45 or 55 overs per side, but now it has been uniformly fixed at 50 overs.
Simply stated, the game works as follows:
- An ODI is contested by two teams of 11 players each.
- The Captain of the side winning the toss chooses to either bat or bowl (field) first.
- The team batting first sets the target score in a single innings. The innings lasts until the batting side is "all out" (i.e., 10 of the 11 batting players are "out") or all of the first side's allotted overs are completed.
- Each bowler is restricted to bowling a maximum of 10 overs (fewer in the case of rain-reduced matches and in any event generally no more than one fifth or 20% of the total overs per innings). Therefore, each team must comprise at least five competent bowlers (either dedicated bowlers or all-rounders).
- The team batting second tries to score more than the target score in order to win the match. Similarly, the side bowling second tries to bowl out the second team or make them exhaust their overs before they reach the target score in order to win.
- If the number of runs scored by both teams is equal when the second team loses all its wickets or exhausts all its overs, then the game is declared a tie (regardless of the number of wickets lost by either team).
Where a number of overs are lost, for example, due to inclement weather conditions, then the total number of overs may be reduced. In the early days of ODI cricket, the team with the better run rate won (see Average Run Rate method), but this favoured the second team. For the 1992 World Cup, an alternative method was used of simply omitting the first team's worst overs (see Most Productive Overs method), but that favoured the first team. Since the late 1990s, the target or result is usually determined by the Duckworth-Lewis (DL) method, which is a method with statistical approach. It takes into consideration the fact that the wickets in hand plays a crucial role in pacing the run-rate. In other words, a team with more wickets in hand can play way more aggressively than the team with fewer wickets in hand. When insufficient overs are played to apply the Duckworth-Lewis method, a match is declared no result. Important one-day matches, particularly in the latter stages of major tournaments, may have two days set aside, such that a result can be achieved on the "reserve day" if the first day is washed out—either by playing a new game, or by resuming the match which was rain-interrupted. The original DL-method however had a few inherent flaws. For example, Duckworth-Lewis-Stern (DLS) method is widely used, which is a modification of the DL-Method suggested by Prof. Steven Stern. It was first implemented during the 2015 World Cup. One of the major changes made to DLS from DL method was based on a historic analysis by Prof. Stern that a team with higher run rate in their initial stages has a greater chance to get to a high score than a team with slow initial run rate, but more wickets in hand.
Because the game uses a white ball instead of the red one used in first-class cricket, the ball can become discoloured and hard to see as the innings progresses, so the ICC has used various rules to help keep the ball playable. Most recently, ICC has made the use of two new balls (one from each end), the same strategy that was used in the 1992 and 1996 World Cups so that each ball is used for only 25 overs. Previously, in October 2007, the ICC sanctioned that after the 34th over, the ball would be replaced with a cleaned previously-used ball. Before October 2007 (except 1992 and 1996 World Cups), only one ball would be used during an innings of an ODI and it was up to the umpire to decide whether to change the ball.
Fielding restrictions and powerplays
A limited number of fielders are allowed in the outfield during powerplays.
The bowling side is subjected to fielding restrictions during an ODI, in order to prevent teams from setting wholly defensive fields. Fielding restrictions dictate the maximum number of fieldsmen allowed to be outside the thirty-yard circle.
Under current ODI rules, there are three levels of fielding restrictions:
- In the first 10 overs of an innings (the mandatory powerplay), the fielding team may have at most two fielders outside the 30-yard circle.
- Between 11 and 40 overs four fielders will be allowed to field outside the 30-yard circle.
- In final 10 overs five fielders will be allowed to field outside the 30-yard circle.
Where a match is shortened by rain, the duration of the powerplays is adjusted to equal 30% of the team's overs wherever possible (20% for the first powerplay, 10% for the second).
Fielding restrictions were first introduced in the Australian 1980–81 season. By 1992, only two fieldsmen were allowed outside the circle in the first fifteen overs, then five fieldsmen allowed outside the circle for the remaining overs. This was shortened to ten overs in 2005, and two five-over powerplays were introduced, with the bowling team having discretion over the timing for both. In 2008, the batting team was given discretion for the timing of one of the two powerplays. In 2011, the teams were restricted to completing the discretionary powerplays between the 16th and 40th overs; previously, the powerplays could take place at any time between the 11th and 50th overs. Finally, in 2012, the bowling powerplay was abandoned, and the number of fielders allowed outside the 30-yard circle during non-powerplay overs was reduced from five to four.
The trial regulations also introduced a substitution rule that allowed the introduction of a replacement player at any stage in the match and until he was called up to play he assumed the role of 12th man. Teams nominated their replacement player, called a Supersub, before the toss. The Supersub could bat, bowl, field or keep wicket once a player was replaced; the replaced player took over the role of 12th man. Over the six months it was in operation, it became very clear that the Supersub was of far more benefit to the side that won the toss, unbalancing the game. Several international captains reached "gentleman's agreements" to discontinue this rule late in 2005. They continued to name Supersubs, as required, but they did not field them by simply using them as a normal 12th man. On 15 February 2006, the ICC announced their intention to discontinue the Supersub rule on 21 March 2006.