Unorthodox cricket bowling has physicists spinning

A team of physicists in Dubai studied the behavior of balls as they travelled through air to explain the bamboozling effect of a controversial technique in cricket known as "round arm" bowling.

Round arm bowling — most recently popularized by former Sri Lankan player Lasith Malinga — is instantly recognizable thanks to its near-horizontal style of delivery.

The bowler releases the ball from the side of the body and head, rather than from above and around the head — the more conventional bowling technique. It's proved challenging for professional batters.

And there's some unique physics at play, according to Siddharth Sudhakaran, a fluid mechanics expert at Amity University Dubai.

Wind tunnel analysis of the 'Malinga slinger'

Sudhakaran led a study into the physics behind this unpredictable bowling style by using a wind tunnel to simulate the movement of the ball.

Using special sensors and imaging equipment, Sudhakaran's group sought to capture the pressure variations surrounding the ball as it traveled through air in the wind tunnel.

They used a brand-new ball that wasn't exposed to degradation from pitch impacts or the arena conditions of a match.

But they were still able to get a glimpse into how a ball spinning at 2,500 revolutions per minute behaves as it travels towards a batter.

Move it like Malinga: Enter the Magnus effect

The secret to the success of Malinga and other, emerging Sri Lankan cricketers, including Matheesha Pathirana and Nuwan Thushara who have modeled their own styles on Malinga's sidearm or round arm technique, appears to be their ability to capture the Magnus effect, a phenomenon studied in physics.

The phenomenon describes how a spinning, spherical object — such as a cricket ball — shifts laterally in the direction of its spin as it travels through air. It is caused by variations in low pressure, surrounding the object as it travels.

It's the same principle used in football. Picture former England star player David Beckham or the film Bend it like Beckham — Beckham would kick the ball in an off-center position to curve it around a defending player and sent it to the back of the net. It's all about spin, and delivery speed. 

"Let's say Malinga is bowling at 90 miles an hour [~145 kmh], he delivers at such a low point and if he's able to give some spin to the ball […] before coming in contact with the pitch, it gets some lateral movement," said Sudhakaran. "It's basically tricking the batsman."

A new edge for pro sportspeople?

Science is everywhere in sport. As with round arm bowling in cricket and curveballs in other sport, it's used to extract every advantage out of human performance.

Professional sport also turns to science to optimize clothing and equipment to deliver a technological edge. But sport isn't about to turn into a science.

Studies like Sudhakaran's wind tunnel experiment are usually done in the absence of a human holding the ball and that can affect the results.

"The lab is like a perfect scenario, so we are using a fresh new ball where the roughness change across the seam is not considered," Sudhakaran said. "[With an old ball] everything is going to be aggravated, so the amount of drift or the lateral movement is going to be different."

But there's no harm in getting your physics degree if you want to outwit your rivals on the pitch.

Edited by: Zulfikar Abbany

Primary source:

Unraveling the near vicinity pressure field of a transversely spinning cricket ball. Published by Aafrein Begam Faazil, Abdul Rahim Farhatnuha, Kizhakkelan Sudhakaran Siddharth in the journal Physics of Fluids (August 2024) https://doi.org/10.1063/5.0215749