Swing bowling in Cricket

For all types of swing:

• The plane of the seam must be vertical with respect to the ground - known as upright seam.
• Backspin must be imparted to the ball so that the seam stays upright and the ball doesn't wobble - this is done with a flick of the wrist at the moment of delivery.

Conventional swing

Ball swings in the direction that the seam points to:

• Outswing: deliver the ball with the seam pointing to the second slip.
• Inswing: deliver the ball with the seam pointing to leg slip.

The side that has relatively more shine should face the batsman.

The side that has deeper embossing must be allowed to become rough and dry (the deeper embossing adds to the roughness). The other side of the ball should be frequently polished to retain the shine as much as possible. 

Reverse swing

One side of the ball must be very rough and dry, and the other must be shiny. Usually it takes 20-40 overs to get the desired level of roughness.

The seam must not be bashed in.

The leading, rough side of the ball must face the batsman.

The ball moves in a direction away from the seam i.e. if seam is pointed towards slips and the rough side faces the batsman, the ball swings into a right-handed batsman.

Interestingly, express fast bowlers may produce reverse swing even with the new ball. The extreme pace (>145kmph) produces the same reverse effect as the roughness in the ball's surface.

Contrast swing

The ball must be held "seam up" i.e. the seam should be vertical and point straight ahead (and not be angled towards the second slip or the leg slip).

One side of the ball must be rough and the other side shiny.

It does not matter if the seam is bashed in.

The speed of the ball determines which way it will swing. For a medium pace bowler, the ball would swing towards the rough side whereas for a faster bowler, it would swing towards the shiny side (you can see how the speed can be varied by a faster bowler to achieve swing both ways).

In street/gully cricket in the sub-continent, contrast swing is achieved by taping one side of a tennis ball. The ball is delivered with the taped side on the left or right.