all about The best Top-spinner in cricket
I’ve started with the top-spinner rather than the stock legbreak as this is by far the easier delivery to describe, so it’s a good starting point. I’m assuming it’s a “pure” top-spinner, i.e. that the seam is vertically upright and pointing down the wicket.
Essentially, all you have to do to work out what the Magnus effect will do with this ball is take the golf ball and turn it upside down, so that instead of pushing the ball up it pulls it down instead.
Now here, for once, I have to take issue with Peter Philpott. In his otherwise flawless book “The Art of Wrist-Spin Bowling” he describes the effect of top-spin (he calls it overspin) saying that “overspin increases the effect of gravity”, a bit of sloppy science that will have all the physics teachers rolling their eyes. The effect of gravity is unchanged throughout – what top-spin does is add an additional effect which accelerates the ball in the same direction. So the ball has the downward acceleration due to gravity AND some more downward acceleration due to the Magnus effect on top of that.
So as the batsman sees the ball come out of the bowler’s hand, he will judge the speed and angle and intuitively estimate where the ball will pitch based on downward acceleration due to gravity alone. Thereafter the Magnus effect will make the ball dip faster in the air, and bounce further away from the batsman than he originally thought it would. That’s not all, however. Because the ball has dipped it will now hit the ground at a steeper angle, and therefore it will bounce higher.
Now anyone who has ever spun a ball onto the floor in front of them will find this last part counter-intuitive. If you gently chuck a top-spinning ball onto the floor in front of you the traction as it lands will accelerate it away from you, making the angle it bounces up at shallower. Likewise a back-spun ball will seem to sit up, and if you give it a really good rip you can even get it to bounce right back towards you despite its original momentum. However – and spinners need to get their heads round this – at any significant speed the Magnus effect’s ability to make the ball hit the ground at a steeper angle and thus bounce harder and higher far outweighs this effect. It’s not that the effect doesn’t exist, after all it’s the same force that makes a leg-break turn, it’s just that it is dwarfed by a counter-acting force in this situation.
So the Magnus effect will make a top-spun ball dip more during flight, meaning it will pitch shorter than anticipated, and hit the ground at a steeper angle, making it bounce higher.