Mushfiqur Rahim's Dismissal

Jasprit Bumrah had Mushfiqur Rahim fending at a delivery outside off stump for a catch in the slips. As commentaros would say, it was a wide enough delivery for Rahim to ignore. It was also short enough to pass over the stumps. He didn’t have to play at it. So why did he?

Sid Monga was on commentary and recorded it as follows:

Monga’s interesting proposition is that the ball swung away after pitching, between pitching and impact. This is a small part of what happened on the delivery. The BCCI’s live ball-by-ball coverage includes a rendering of the ball-tracking record of each delivery. The summary of the ball-track which is sent to your browser to produce the rendering is here.

The toplines for this delivery:

Length 7.7m
Swing: -0.321 deg. (-ve sign implies movement from leg to off for the right hand bat)
Seam: 0.134 deg. (+ve sign implies movement from off to leg for the right hand bat)
release speed: 87.0 mph
post-bounce speed: 33.5 m/s (75 mph)
post-bounce lateral acceleration: -5.57 m/s^2 (from leg to off)
reaction time to interception: 0.484 seconds.
vertical component of acceleration before pitching: -5.57 m/s^2

This vertical acceleration is made up of gravity (-9.8m/s^2) and a magnus force which is created due to the amount of backspin on the ball. Bumrah and Pat Cummins, among contemporary bowlers generate unusually high amounts of backspin. The magnus force for this delivery is +3.8 m/s2. Overspin, which spinners typically impart gets the ball to dip. For spinners, the vertical acceleration before pitching tends to be about -10 to -11 m/s^2. For most fast bowlers it is typically between -6 and -7 m/s^2.

After pitching, the ball seamed inwards marginally. It also swung outwards, as the post-bounce lateral acceleration suggests. The net effect of this was somewhere between 2.0cm and 2.5cm in lateral movement away (the effect of the swing is about 7.5-8 cms outwards, the effect of the seam is about 5.5-6cm inwards) from the batter (compared to where the ball would have been if there was no seam or post-bounce swing). It is not easy to observe just by looking at the delivery even in super slow-motion (the net movement is just over one tenth the width of the stumps). Note that the “Swing” listed above refers to swing before the ball pitched. The batter has about 0.17 seconds from the time the ball pitches to the time that it reaches him.

But this movement, marginal as it was, wasn’t what trouble the batter. Mushfiqur was essentially beaten by the length. As he lined up that ball, he thought it was going to be short of a good length, and wide, and the forcing shot off the back foot was on. The backspin which Bumrah gets increases the length (at the speed at which Bumrah bowlers, this increase is somewhere between 1 and 2 feet for a good length) and turns what looks to the batter to be a short and wide delivery, to be a good length delivery (7.7m is a good length for a fast bowler). What makes it worse is that this happens as the batter is setting up to play the imagined original length. This is essentially the fast bowler’s what happens when a spinner gets the ball to dip on the batter too.

Some bowlers get the batter to fend the ball to slip from that widish line more often than other batters. Batters lose shape more often against some bowlers than others. This backspin is probably why.