In the sport of cricket an over is a series of six consecutive balls bowled by a single bowler. No bowler is allowed to bowl in consecutive overs.\n\nSpecifically, an over must consist of six legal deliveries. No balls and wides do not count as one of the six balls in an over.\n\nIn one-day cricket bowlers are restricted to the total number of overs they may bowl in a match and the length of the game is determined by the total number of overs bowled (usually 40 or 50 per innings). In Test and county cricket, teams are usually required to bowl a minimum number of overs per day to prevent spoiling of the game by a slow over rate.\n\nEach consecutive over is bowled from the opposite end of the pitch ensuring that both batsmen face the bowling.\n\nA maiden over is one in which no runs are scored.\n\nTactical considerations in bowling overs\n\nThe over is a fundamental unit in the tactical planning of the fielding side. Since a single bowler has six, and only six, legal balls before another bowler must bowl, he typically plans to use those six balls to set up a pattern of play designed to get a batsman out. For example, bowling a few balls with a repetitive line, length, or spin, followed by a variation designed to surprise the batsman.\n\nEarly in the over the bowler may tempt the batsman into scoring runs by providing balls that are relatively easy to hit. If the batsman takes the bait, the bowler can follow up with a variation designed either to hit the wicket or induce a catch. A batsman still in aggressive run-scoring mode may make a mistake playing the ball and end up losing his wicket.\n\nThe captain of the fielding team decides which bowler will bowl any given over (subject to the restriction that no bowler may bowl two overs in succession). Generally two bowlers will alternate overs from opposite ends of the pitch, until one tires or becomes ineffective, at which point the captain will replace that bowler with another. A period of bowling every second over like this is called a spell of bowling.\n\nTactical considerations in batting\n\nIf the two batsmen are not similar, tactical considerations may affect their play. If one batsman is stronger than the other, they may attempt to engineer their scores so that the stronger batsman faces the bowling more often. This may take the form of the stronger batsman trying to score an even number of runs on early balls in the over and an odd number on the last ball; the weaker batsman will attempt the reverse, and the bowler will try to disrupt this pattern.\n\nIf one batsman 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.\n\nHistorical number of balls per over in Test cricket\n\nModern day Test cricket (since 1979/80) has been played all over the world with six balls per over. However, Test cricket started with 4 balls per over and has had varying number of balls per over around the world upto 1979/80.\n\nBalls per over\n\nIn England\n\n1880 to 1888: 4 \n1890 to 1899: 5 \n1902 to 1938: 6 \n1939  : 8 \n1946 to date: 6 \n\nIn Australia\n\n1876/77 to 1887/88: 4 \n1891/92 to 1920/21: 6 \n1924/25  : 8 \n1928/29 to 1932/33: 6 \n1936/37 to 1978/79: 8 \n1979/80 to date  : 6 \n\nIn South Africa\n\n\n1891/92 to 1898/99: 5 \n1902/03 to 1935/36: 6 \n1938/39 to 1957/58: 8 \n1961/62 to date  : 6 \n\nIn New Zealand\n\n1929/30 to 1967/68: 6 \n1968/69 to 1978/79: 8 \n1979/80 to date  : 6 \n\nIn Pakistan\n\n1954/55 to 1972/73: 6 \n1974/75 to 1977/78: 8 \n1978/79 to date  : 6 \n\nIn India, West Indies, Sri Lanka, Zimbabwe, Bangladesh and United Arab Emirates (venue, not host) all Test matches were played with 6 ball overs.