in cricket, what constitutes an "over"?

Answer 1

In the sport of cricket, an over is a set of six consecutive balls bowled in succession. An over is normally bowled by a single bowler. However, in the event of injury preventing a bowler from completing an over, it shall be completed by a teammate.

An over must consist of six legal deliveries. No balls and wides do not count toward the six-ball tally. The 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).


For more details, please check the following link:

http://en.wikipedia.org/wiki/Over_(cricket)

Answer 2

Tactical considerations in bowling overs

The over is a fundamental consideration in the tactical planning of the fielding side. Since a single bowler has six, and only six, legal balls to bowl before he must hand the ball to another bowler, he typically plans to use those six balls to set up a pattern of play designed to get a batsman out. For example, he may bowl the first few balls with the same line, length, or spin. He intends to tempt the batsman into scoring runs by providing balls that are relatively easy to hit. If the batsman takes the bait, the bowler can then follow up with a variation designed to hit the wicket, or a ball that is intended to induce a mistake from a batsman who is still in aggressive run-scoring mode, which will result in him being caught out. The latter type of delivery is known as a sucker ball.


Tactical considerations in batting

If 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 scoring 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.

If 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.


Historical number of balls per over in Test cricket
Modern 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 up to 1979/80.

Balls per over

In England

1880 to 1888: 4
1890 to 1899: 5
1902 to 1938: 6
1939 only : 8
1946 to date: 6

In Australia

1876/77 to 1887/88: 4
1891/92 to 1920/21: 6
1928/29 to 1932/33: 6
1924/25 and 1936/37 to 1978/79: 8
1979/80 to date: 6

In South Africa

1891/92 to 1898/99: 5
1902/03 to 1935/36: 6
1938/39 to 1957/58: 8
1961/62 to date: 6

In New Zealand

1929/30 to 1967/68: 6
1968/69 to 1978/79: 8
1979/80 to date: 6

In Pakistan

1954/55 to 1972/73: 6
1974/75 to 1977/78: 8
1978/79 to date: 6

In India, West Indies, Sri Lanka, Zimbabwe, Bangladesh and the United Arab Emirates (venue, not host) all Test matches have been played with 6 ball overs.

Answer 3

When a bowler bowls 7 balls as per rules, it constitute an over. Then another bowler starts bowling.
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