A maiden over is an over in which no runs are scored that count against the bowler (so and byes may be scored as they are not counted against the bowler). A wicket maiden is a maiden over in which a wicket is also taken. Similarly, double and triple wicket maidens are when two and three wickets are taken in a maiden over.
After six deliveries the umpire calls 'over'; the fielding team switches ends, and a different bowler is selected to bowl from the opposite end. The captain of the fielding team decides which bowler will bowl any given over, and no bowler may bowl two overs in succession.
During the middle of an over, in the event that a bowler is injured or is sent out of the attack by the umpire (for disciplinary reasons, such as bowling beamers), a teammate completes any remaining deliveries.
Because a bowler may not bowl consecutive overs, the general tactic is for the captain to appoint two bowlers to alternate overs from opposite ends. When one bowler tires or becomes ineffective, the captain will replace that bowler with another. The period of time during which a bowler bowls every alternate over is known as a spell.
In limited overs cricket matches, bowlers are generally restricted in the total number of overs they may bowl in a match. The general rule is that no bowler can bowl more than 20% of the total overs per innings; thus, in a 50-over match each bowler can bowl a maximum of 10 overs.
In Test cricket and first-class cricket, there is no limit to the number of overs in a team's innings, nor is there any limit to how many may be bowled by a single bowler. In these matches, there is a requirement to bowl a minimum of 90 overs in a day's play, to ensure a good spectacle, and to prevent the fielding team from wasting time for tactical reasons.
Cricket imposes penalties if a team bowls its overs at a very slow over rate, such as fines, loss of competition points, and match bans. If a team is proceeding slowly, some captains will choose to use slow/spin bowlers. Such bowlers have a shorter run up so they complete their overs more quickly. Often this means choosing an inferior strategy by employing a less skilful bowler to avoid penalties that are perceived to be greater, such as being banned or losing points.
If one batting player is right-handed and the other left-handed, they may try to score odd numbers of runs to disrupt the bowling pattern and tire the fielders by making them reposition themselves frequently.
Prior to the Laws of Cricket (1980 Code), law 17.1 (Number of balls in) did not explicitly specify the number of balls to be bowled in an over, but merely stated that the number of balls should be agreed by the two captains prior to the toss. In practice, the number of balls was usually stipulated in the playing regulations governing the match being played. Although six was the usual number of balls, it was not always the case. From the 1980 code onwards, law 17.1 was amended to read, "The ball shall be bowled from each end alternately in overs of 6 balls".
Balls per over
In South Africa
In New Zealand
In India, West Indies, Sri Lanka, Zimbabwe, Bangladesh, the United Arab Emirates (venue, not host) and Ireland all Test matches have been played with six ball overs.