Saliva may not be the only reason we're seeing reverse swing this IPL

Rajasthan Royals (RR) have had their mental fortitude questioned this season to the extent that pundits have been criticising their decision to chase even when it is plain to see they should. This kind of message comes with the territory: you play a popular league, you fail to close out two matches from nine required in the last over, and the first diagnosis is likely to be around mental strength and the first prescription is to tell you to stop doing what you have been doing.

We can't fact-check the pundits. There could well be a block for all we know. However, what we know and can verify is that in both those games the ball reverse-swung appreciably, playing a part in what is popularly known as "chokes".

Mitchell Starc started the turnaround in the Delhi Capitals (DC) game. The ball to get a set Nitish Rana swung in 1.83 degrees. On average, Starc drew 1.2 degrees of swing in his last two overs as opposed to 0.8 in his first two with the new ball.

Lucknow Super Giants' (LSG) Avesh Khan's last two overs to deny RR featured even more reverse swing. The yorker to get Yashasvi Jaiswal swung 2.21 degrees. The yorker to beat Riyan Prag's ramp swung 1.86.

There is enough anecdotal evidence of reverse swing this IPL at various ages of the ball. If Starc and Avesh swung it right at the end, there was a game when Sunrisers Hyderabad's (SRH) Eshan Malinga reversed the ball in the 12th over and then right at the end. In the 18th over, he swung two balls at 2.59 degrees each, and took out Mumbai Indians' (MI) Naman Dhir's toe with one that swung in 1.84 degrees. Last year, 11% of deliveries, excluding slower balls, swung more than 1.5 degrees after the tenth over; this year 18%. It has almost gone from one in ten to one in five.

However, before we conclude that there has been more reverse swing than the Covid-19 years, when the use of saliva to shine the ball was banned, we need to first acknowledge that degrees of swing is a flawed measure. The average swing is even worse. Aaron Briggs, a sports aerodynamist who has done a PhD in the aerodynamics of swing bowling, has been advocating a "swing coefficient", which measures swing independent of the time the ball spent in the air.

The fuller you bowl, the more chance you give the ball to swing. So the degrees need to be normalised for length for it to be comparable. That, though, is the easier part. Briggs points out a bigger drawback in data collection in cricket: we don't record the bowler's intent or skill. We don't yet record different seam orientations bowlers try. Did the bowler really intend to swing the ball? Was the release good? To account for that, the best we can do is exclude slower balls.

Himanish Ganjoo, a physicist and data scientist, made the data somewhat comparable by normalising the degrees of swing for length. He considered only balls bowled at more than 128kph, and the following graphic emerged.

There have indeed been periods of significantly higher reverse swing this year. Briggs warns against oversimplifying this by correlating it with the lifting of the saliva ban. He says comparing reverse swing this year with pre-saliva-ban years will not provide any intelligence because the Kookaburra ball has itself evolved over the years.

Briggs' experiments have shown that more than the shine, the rough is a non-negotiable for reverse swing. The reverse swing is a function of how long the air sticks to the two sides of the ball. What you are basically doing is flinging the ball into an air tunnel. When the ball is perfectly smooth, air separates around the middle of the ball. As it gets rougher, this separation point moves to the back of the ball. When it gets even rougher - dirty, shammy rough as opposed to fluffy rough - this separation point moves forward. So if you have one side really dirty and rough and the other side less rough, the air on either side is separating from the ball at the two extremes, thus kicking the ball sideways.

This is where shining agents - sweat, saliva, Vaseline, rubbing the ball on pants, etc - come in. This is how Wasim Akram has explained reverse swing to me over two different interviews. He didn't use to mess with the new ball. Just use the conventional swing when it is still new. Once convinced there is no new-ball help left, start getting the ball really rough, it doesn't matter which side. Once you have got the ball rough, identify the rougher side and start shining the less rough one. And now it takes all the discipline to not let even one drop of sweat fall on the rough side.

Now there are two big differences between that reverse swing and what we are seeing in the IPL. Firstly, it had the time for the ball to go rough before they could, in the words of Briggs, repair one of the sides. Twenty overs is hardly enough time for that to happen. More importantly, the red ball is polished, which can be re-shone with sweat or saliva. The white ball is painted; it cannot be repaired with sweat or saliva. The weight differential doesn't even factor in because if one side is heavier, it will tilt down as opposed to move sideways.

It's the rougher squares this year, something the bowlers confirm they have encountered, that have fulfilled the first precondition even in a span as short as 20 overs. Without that roughness, saliva or sweat makes no difference. To Briggs, saliva over sweat is not a big difference either. He suspects it could be a self-fulfilling prophecy that bowlers, who believe saliva makes a difference, are attempting reverse swing more often, and thus getting it more often.

On the field, the bowlers differ. "There is no way we don't try everything even with just sweat," says one. Saliva, though, has two advantages. It is more viscous than sweat, and human bodies have a much larger supply of saliva than sweat. Now what the bowlers do is that they load one side of the ball with saliva, especially pucking it up where the quarter seam splits. And the quarter seam splits easily: one boundary into the LED boards and it is done. The bowlers load the seam split believing it makes one side heavier.

"In 70% of the games, the ball is tailing in and it's only because the saliva is heavy, and our sweat is not so heavy," Mohit Sharma said recently. "If the ball is heavier on one side, it will tail in."

Briggs concedes that if the saliva is sugar-laden through candy or mint, it is possible that it forms a smooth layer over the rough, creating different degrees of roughness on the two sides. "We anyway never shone the old ball with sweat," one bowler says. "Sweat was used only on the new ball. For the old ball, you need saliva. Saliva plus mentos is the bomb."

To do that, though, will require a shrewd practitioner of managing the ball because umpires will not allow a player who has anything in their mouth to spit on the ball. Then again, it is not so strictly policed. A player could go off the field, have a lozenge, not bring the smoking gun onto the field, but the saliva will be thick and sugary for a while. Players are known to go off, apply Vaseline on their fingers and come back to shine the ball, but it is difficult to catch them red-handed. Given the stigma around ball-tampering, any action must be solid enough to stand the scrutiny of a court of law.

Still, the administrators and umpires needn't worry too much: the shine is of no use by itself, especially on the white ball. If the square is not dry and rough, the ball is not likely to reverse. This is why the umpires frown upon throws on the bounce. Anything from inside 30 yards must be sent in on the full, the only exception being a genuine run-out chance on a direct hit.

All said and done, though, the scoring rates haven't dropped. Fast bowlers went at 11.43 per over at the death last year, this year it is 11.52. Expand it to the last ten overs, and the economy rate for pace bowlers has gone up from 10.49 to 10.58. In the first 50 matches this IPL, spinners have bowled 41% of the overs as opposed to 33% in the first 50 matches last year.

For one, it is still small reverse swing, not the big, booming yorkers we have in our minds. So the impact is limited, which is not to say there is no impact. Ganjoo tells me that fast bowlers are attempting yorkers 42% of the time at the death this year as opposed to just 36% last year. The real advantage they have is that when they miss their length, they get saved by reverse swing. At the death this year, the strike rate on slot balls that swing less than 1.5 degrees is 161, but for those that swing more than 1.5 degrees, it is 121.

It is a fact that bowlers have little agency in this format against batters with high intent, high resources and ever-improving hitting efficiency, but evidence suggests that whatever little reverse swing the bowlers have found has limited the damage a little bit. Also, not every square is rough, so not everyone can reverse. Therefore, overall numbers are not the best indicator. It is a tribute to the bowlers' ingenuity that the moment they find conditions suitable for reverse, they manage to do so even in a 20-over game.