Over (cricket)

In the sport of cricket, an over is a set of six balls bowled from one end of a cricket pitch.

In a normal over, a single bowler delivers six balls in succession, from one end of the pitch, to the batsman at the other end. After six deliveries, the umpire calls 'over'; the fielding team switches ends, and a different bowler is selected to bowl an over from the opposite end of the pitch, while the batsmen do not change ends. The captain of the fielding team decides which bowler will bowl any given over, and no bowler may bowl two overs in succession.

An over must consist of six legal deliveries. If the bowler bowls a wide or a no ball, that illegal delivery is not counted towards the six-ball tally, and another delivery will need to be bowled in its place.

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), during the middle of an over, a team-mate 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, such as one-day cricket (for example, a One-Day International, "ODI") and Twenty20 ("T20"), each team has one batting innings, which ends either after all wickets are lost or when the allotted overs are completed. In such a match, bowlers are generally restricted to 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 allotted overs per innings; thus, in a 50 overs match each bowler can bowl up to a maximum of 10 overs.

In Test and first class cricket, there is no limit to the number of overs which may be completed in a team's innings, nor is there any limit to the number of overs which may be bowled by a single bowler. In these matches, there is a requirement to bowl a minimum of ninety overs in a day's play, to ensure a good spectacle, and to prevent the fielding team from wasting time for tactical reasons.

...
Wikipedia