How ball-tampering favours bowlers

By keeping one side of a cricket ball shiny and smooth, bowlers can swing the ball in the air. After 60-70 overs the surface of the ball becomes unevenly battered, and reverse swing becomes possible


Normal swing
Ball held with shiny side towards batsman, seam points in direction ball will swing

Normal out-swing

Out-swinger
Seam points to slip (batsman’s right)

In-swinger
Seam points towards fine leg (batsman’s left)

Reverse in-swing

Out-swing

In-swing


1. Boundary layer: Thin layer of air forms around surface of ball

2. Rough side: Air flow is turbulent due to seam of ball – causing rapid fluctuations in pressure

3. Smooth side: Higher air pressure swings ball in direction of seam

4. Boundary layer: Turbulent air flow extends to both sides of ball

5. Smooth side: Air speed slows – air pressure falls

6. Rough side: Higher pressure causes effect of seam to be reversed, swinging ball towards batsman


Law 41.3.2: Offence to interfere with surface or seams, or alter condition of ball in any way

Allowed: Players can polish ball on their clothes, dry wet ball, or remove mud from ball under
supervision of umpire

Tampering: Sucked sweets, lip gloss, Vaseline or hair wax all used to make smooth side shine

Rubbing grit into quarter seam to make rough side rougher, gouging or use of sandpaper banned

Rough side
Low pressure
Smooth side – air travels faster

Rough side towards batsman

Quarter seam

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Sources: Lords.org, Law 41 – Unfair play, Scienceabc.com
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