The outswinging delivery moves away from the right-handed batsman, while the inswinger moves in towards him. Normal swing is achieved by maintaining laminar boundary layer air-flow on the shiny side whilst creating turbulent flow on the seam side. These deliveries, particularly the outswinger, are the bread and butter of opening bowlers who get to use the ball while it is still new. Reverse Swing Reverse swing is very different to conventional swing. Although the seam is oriented in the same way as for an outswinger and the action is the same, the rough side of the ball is to the fore, and the ball moves in to the batsman like an inswinger.
Reverse swing is achieved when the ball is bowled very fast.
In this case the air flow will become turbulent on both sides before it reaches the seam. Despite being widely observed in practice, there is currently no theoretical, or experimental, evidence for humidity having any affect on the amount of swing. Experiments in wind tunnels show no noticeable difference in the amount of swing between dry and humid air, and there is no measureable aerodynamic difference in the state of the ball due to moisture. There are several possible explanations for late swing - where sideways movement occurs only late in the ball's flight. It is an illusion.