The magician's wrist: how Bumrah does what he does

Just 47 Tests and 89 ODIs to go along with 245 T20 games, and Jasprit Bumrah is already in the conversation to be one of the greatest all-format bowlers ever. He has displayed mastery over a wide oeuvre of skills across situations and conditions, with the red ball and white, especially after his return from injury in 2023.

Much has been said about Bumrah's unique action, heavy with hyperextension in his bowling arm, and his abnormal release point, about 50 centimetres closer to the batter than other top bowler's releases. In all this, his wizardry with the seam is seldom discussed. Bumrah puts more revs on his backspinning pace-on deliveries than most fast bowlers do, and this has a multitude of effects. Yes, he bowls at a good pace, hits the good length like a machine, and plans and delivers his multiple variations almost perfectly. But the action his wrist imparts on the seam, almost imperceptibly, adds layers of difficulty on top of his extremely strong fundamentals.

Because of his hyperextended front arm, Bumrah has to give the ball an almighty whip at release to keep his wrist upright and propel the ball forward. This whip bestows the ball with high backspin. This backspin causes the ball to feel an extra upward force before landing. This phenomenon, called the Magnus effect, is what causes dip when spinners bowl overspin. For seam-up deliveries, it happens in the opposite direction.

The plot above shows the distribution of vertical acceleration for pace-on balls (130-plus kph) from the IPL seasons of 2022 to 2024. Since the ball is accelerating downwards while falling, the numbers on the X axis are negative. Here, a number closer to zero indicates more upward force on the ball. Notice how Bumrah's distribution peaks significantly to the right of the distribution for all other fast bowlers - indicating that he generates significantly more upward force than others. He is much likelier than others to deliver a ball with high upward force. This extra upward force is the direct result of the amount of backspin on the ball.

The higher upward force makes the trajectories of his deliveries slightly flatter than those of others before pitching, which possibly has a direct effect on the efficacy of his fuller balls. The plot below shows the batter's strike rates for full tosses, well-executed yorkers, and slot balls in the last five overs in the IPLs of 2022-2024. While the average bowler goes for plenty when they miss the yorker, Bumrah concedes runs at a batting strike rate of lower than 120 even when he overpitches or underpitches.

Some of this is due to his reputation - batters look to play him out. Some of it is due to his anomalous release: his release point varies almost negligibly between full and good-length balls, and some of it is due to the "lift" he gets from the Magnus force, making his full deliveries scoot through the air flatter, messing up the contact points of a batter looking to hit him.

This heavy backspin also contributes indirectly to swing by helping the seam stay upright in one plane. Much like with a bicycle wheel, the faster the backspin, the more stable the seam. With the new ball, Bumrah can angle the seam slightly either way to get the ball to swing in the direction he wants it to. Owing to the revs on it, the seam seldom wobbles, creating perfect conditions for swing. Of course it is a testament to his powers that Bumrah can land the ball perfectly on a good length and line while switching the direction of swing mid-over. With the old ball, Bumrah relies on the difference in the roughness of the two halves of the ball, keeping the seam upright and switching the shiny side.

The plot below shows the distributions of how much Bumrah swings the new and old balls, considering data from Tests in India from 2023 through 2024. With the new ball (first 20 overs), you see two bumps either side of the "no-swing axis" at around 3 and -3 degrees, showing a small proportion of high-inswing and outswing deliveries. Compare that to the distribution with the old ball. The amount of swing is lower - the peaks are at about 1.5 degrees on both sides (old-ball swing is less in magnitude than new ball swing). But the peaks are much higher than the new ball peaks. Which means he bowls swinging deliveries much more often with the old ball than the new. With both, he manages to swing them both ways. It's the skill of his hands and fingers, coupled with the extremely stable seam, that enables this kind of swing profile.

Bumrah's backspin causes a flatter trajectory than is usual for other bowlers, as we have seen. In addition, his release heights are somewhere close to the average for fast bowlers (around 2 metres). These two things together mean that the vertical speeds of his deliveries before pitching are lower than those of the average bowler. The higher your vertical speed is, the harder you hit the pitch, and the greater the misbehaviour you can extract. And yet, Bumrah bowls more high-seaming balls than other bowlers. This is a result of his impeccable seam presentation, hitting the seam almost every time he bowls. But it also results from his high backspin rates.

The plot below shows the percentage of balls in different ranges of seam movement by Bumrah and other fast bowlers in Tests played in India from 2023 through 2024, only considering fast balls (130-plus kph). Balls seaming more than half a degree are usually troublesome for batters, with little time to adjust the path of the bat to cover the lateral movement. In every seam range for 0.5 degrees or higher, Bumrah has a higher percentage of balls than other fast bowlers. This is a direct result of the extreme backspin on the ball.

Flatter trajectories, high seam, perfect swing - Bumrah's high backspin already imbues his deliveries with lethal characteristics, but it also gives them anomalous bounce. This aspect is almost never talked about, perhaps due to the difficulty of gauging it without data. Despite the flatter path and lower release point, Bumrah's deliveries bounce more than the average bowler's. The plot below shows the median height when the ball reaches the plane of the stumps, using the same Test data set as above.

In the 5-9 metre lengths, which are the good and "hard" lengths, Bumrah's deliveries reach the stumps about 5 centimetres higher than the average pacer's deliveries. This might look like a minor difference but it is what makes him bowl the "heavy ball", which hits the bat a smidgen higher than expected. His unusual late, low release already throws the batter off instincts developed over years of training; that and the slightly higher bounce makes it tough to make ideal contact. Since changing the vertical motion of the bat involves working against gravity, adjusting to even small changes in bounce are the toughest skill for a batter to develop, after adjusting for high seam movement.

But what is happening here? If you hit the pitch flatter, like Bumrah does, you should get lower bounce than others. That is what convention says. But Bumrah upends conventional logic here too. The backspin on his balls is so high that it overpowers the effect of the flat path and low release.

Consider a slow tennis shot hit with backspin. Tennis players and fans know that slow backspinning shots bounce higher. The spin on the ball causes friction with the surface, zapping the ball of its low forward speed. The vertical speed, however, does not get cut too much in comparison. What we call "steep bounce" is actually a measure of how much vertical speed the ball has compared to forward speed. A ball that loses relatively more of its forward speed on bouncing will appear to stop and bounce more (hence the term "tennis-ball bounce"). Upon contact with the surface, the high backspin, paired with the relatively low speed, reduces the forward speed much more than it does the vertical speed. (Thanks to Aaron Briggs, aerodynamicist and analyst with the ECB, for this insight.)

The reduction of forward speed happens for all bowlers' deliveries, but in Bumrah's case, his extreme backspin dominates the interaction with the pitch. Consequently, despite his low vertical speeds before pitching, he gets more bounce than average. The backspin makes such a violent impact that it takes away more of the forward speed, making the ball rise steeper than with the average bowler.

It is important to clear up a common misconception here. In cricket, spinners bowling with overspin obtain more bounce. This is because overspin makes the ball dip and land harder into the pitch. The opposite happens with pacers, who generate backspin: their deliveries land flatter on the pitch. In this regard, in terms of what backspin and overspin do to the ball in the air, the former lowers the bounce and the latter enhances it. However, the phenomenon seen with Bumrah here results from the interaction of the ball with the pitch. When the ball makes contact with the surface, backspin adds to bounce, while overspin reduces it. This pitch interaction effect is too minute to see for most deliveries, but it is the relevant effect here.

In the air, before pitching, backspin does make Bumrah's deliveries flatter. The plot below shows the average angle that the ball makes with the ground before pitching for different lengths, comparing Bumrah with other bowlers (same Test match data as above). For all lengths from 2 to 8 metres, Bumrah has a lower angle than the average bowler, which means his deliveries land flatter than the average bowler's deliveries.

The next plot shows the ratio of the post-bounce angle to the pre-bounce angle. This effectively measures not only the steepness of the ball after pitching, it also tells us how the vertical and forward speeds of the ball relate to each other before and after pitching. A higher ratio means that the ball gets steeper on account of losing more forward velocity than vertical velocity, all relative to the velocities before pitching. Here, Bumrah is higher than the average pacer in all lengths from 3 to 9 metres. This is strong evidence supporting the "tennis ball bounce" explanation for why Bumrah gets higher bounce than average despite his pre-bounce trajectories.

Cricket is a game of "usualness". Batters train for thousands of hours, tuning their internal prediction systems to react to deliveries from an usual distribution of angles, with usual distributions of movement, release, and bounce. Any aberration disturbs this training. Bumrah is a unique confluence of anomalies in addition to rare cricketing nous and almost superhuman skill, making him the almost perfect bowler. While his late release is discussed ad infinitum, it is his extreme whippage on the seam of the cricket ball that unleashes a torrent of little anomalies - in the air, off the pitch, laterally and vertically, overcoming the limitations of conditions or format, at nearly 90 miles per hour. Everything, everywhere, all at once.