Off theory involves concentrating the line of the bowling attack just outside the off stump. This area is often referred to as the 'corridor of uncertainty', as unless a batsman knows exactly where his off-stump is, he will have to play a shot at any ball bowled there. (Not to do so runs the risk that the ball will hit off-stump, which would not only get the batsman out but leave him looking extremely foolish.) The attack is supported with several fielders in a cordon of catching positions behind the wicket on the off side. The aim is to entice the batsman to play at the ball with the bat away from the body ('fishing outside off-stump'). This provides several ways in which the batsman can get out:
Originally developed in the late 19th century as an alternative to bowling directly at the wicket in an attempt to get batsmen out bowled or leg before wicket, off theory led to the rise in importance of slips and gully fielders as dedicated catching positions. The tactic has evolved until the modern day, in which the usual line of attack by fast bowlers is somewhat further outside off stump than it was typically in the 19th century.
Off theory - although not commonly known by that name now - has become the most common attacking bowling tactic used in cricket. It has thus developed many nuances and can be a ball-by-ball tactical struggle for supremacy between the bowler and batsman that many cricket fans find gripping when executed by a skilled bowler.