March 19, 2017

The mystery of the knuckleball

Rabi Mehta and Garfield Robinson
The baseball pitch that could free cricket's bowlers from the shackles that tie them down
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Even knuckleball expert Phil Niekro doesn't know exactly how the unpredictable delivery works © Getty Images

Flatter pitches, fatter bats, shorter boundaries, fielding restrictions, free hits and Powerplays have all resulted in higher batting averages and faster scoring rates. Not that long ago, anything over four runs per over would have been considered expensive in a 50-over game. But on commentary during the last World Cup, Michael Holding said he would be happy conceding six runs per over if he were playing currently. Two hundred and fifty used to be a highly competitive one-day total; nowadays totals approaching 400 are not uncommon.

While batsmen have been feted and fattened, bowlers have been left to fend for themselves and to rely on their own resourcefulness.

Reverse and contrast swing, once viewed with suspicion, are now vital weapons for bowlers capable of harnessing them. Mystery spin, featuring the doosra, was another attempt at making the playing field more even. Unfortunately the doosra has recently fallen on hard times following the crackdown on illegal bowling actions. It has now got to the point where it is difficult to name even a single international bowler still trading in the delivery.

Here is another suggestion for them to consider: how about taking a look at the mysterious pitch in baseball known as the knuckleball?

Often referred to as "unhittable" because of its unpredictable movement, the knuckleball also presents a challenge to catchers, and to umpires determining balls and strikes.

Apart from being a baseball Hall of Famer, Phil Niekro is the game's foremost authority on the knuckleball. Asked what a knuckleball is, he responded, "I've been trying to figure that out. I'm still trying to figure that out."

The pitch is thrown in such a way as to almost totally eliminate spin on the ball. The ball is not gripped by the knuckles, as the name suggests, but by the fingertips. At the point of release the fingers are extended outwards in an attempt to minimise any kind of rotation. The knuckleball, or knuckler, will sometimes move in more than one direction before it reaches the batter.

As the ball flies, a thin layer of air, called the "boundary layer", forms along its surface. This layer cannot stay attached to the ball's surface all the way around, so it tends to leave or "separate" from the surface at some point

"When a knuckleball pitcher is on," said baseball writer Lew Freedman, "that ball with no spin might suddenly take off in a fresh direction to the right and then turn back to the left. The batter keeps his eye on the ball but cannot believe what it is doing, seeming of its own volition."

Football fans might have witnessed a few spectacular "knuckleball" goals. Usually scored from a distance, the ball appears to change direction randomly, leaving the goalkeeper with little chance. Kicked with very little spin, the unpredictable movement is the result of what is usually labelled the "knuckle effect." This was most evident in the 2010 World Cup when the players constantly complained about the excessive knuckling of the Jabulani ball.

Since it is normally thrown at between 65mph and 75mph approximately, a knuckleball that fails to knuckle will be relatively easy to hit. To make good connection with one that is well delivered, however, batters rely on one thing: luck. Unsurprisingly, whenever batters manage to hit one, they often admit that it is more a case of ball hitting bat than the other way around.

Admittedly, transferring the knuckleball technique to cricket may present challenges. There are only slight differences between the balls used in each sport in terms of size and weight, but the cricket ball is harder and has a shinier finish when new, which probably makes it more troublesome to grip. Additionally, the seam patterns are dissimilar, which will result in dissimilar aerodynamic forces on the ball. Cricketers could find that the straight-arm bowling action is less amenable to delivering a ball that does not rotate than the pitching action in baseball.

On occasion, balls bowled by the West Indies spinner Sunil Narine have been described as knuckleballs. What is clear, however, is that they are not knuckleballs of the baseball type, as there is too much rotation. However, there is video evidence that the former Indian fast bowler Zaheer Khan was able to develop a slower delivery with very little spin on the ball.

The knuckleball grip © Getty Images

So what is the science behind the knuckling effect?

As the ball flies, a thin layer of air called the "boundary layer" forms along its surface. This layer cannot stay attached to the ball's surface all the way around, so it tends to leave or "separate" from the surface at some point. The location of this separation point determines the pressure on either side of the ball, and a relatively late separation results in lower pressure on that side. A side force, or swing, will only be generated if there is a pressure difference between the two sides of the ball. The seam on a baseball or cricket ball acts to disturb the boundary layer, and hence affects at what point the separation occurs.

As the very slowly spinning ball is flying through the air, the rotating seam will affect the boundary layer in different ways on different parts of the ball. This results in a side force whose direction and magnitude vary over the course of the flight, causing the ball to knuckle.

Another feature of the ball with very little spin is that it will drop more precipitously than a delivery with backspin. Zaheer's knuckleball, for example, was observed to dip sharply since there was no upwards Magnus force - which backspin provides - to oppose the pull of gravity.

It is likely that bowlers will need to train a lot to get adept at delivering a knuckleball. Once mastered, however, the delivery should yield significant dividends. Spinners could use it as a variation, fast bowlers as a slower ball. Or, as is the case with pitchers in baseball, some bowlers could use it as their sole stock in trade.

Imagine the first true knuckleball bowler in operation in an international match with the ball dancing and dropping in ways not previously witnessed in cricket. It would probably cause as much consternation as when Bernard Bosanquet first unveiled the googly.

Bowled well, the knuckleball should prove difficult to negotiate, as there would be no method to the movement of each delivery - at least none that anybody is able to predict. That should be motivation enough for bowlers to try mastering it.

Rabi Mehta is a sports aerodynamics consultant in California. Garfield Robinson is a freelance cricket writer @spiider10

Comments have now been closed for this article

  • tobym66604041 on March 21, 2017, 16:27 GMT

    I think you'll find Alan Connolly was a Test cricketer who bowled the knuckle ball.

  • mahjut on March 21, 2017, 14:23 GMT

    @mightrysparrow ... maybe not on the team but a disadvantage on the bowlers for sure! Watching Steyn get spanked for 22 runs in a T20 over is heart-breaking especially when you consider all things being said about the bloated batters, just how good he, and any other bowler still keeping their ave below 25, are! One may be tempted not to sympathise (it's well paid and a choice after all - T20 leagues I mean) but that's exactly the point (well, my point anyway) - with T20 being so lucrative and all these kids loving watching ball ricocheting to boundary then what is the future of bowling? Which self respecting bowler wants to get paid to be batsmans' fodder?

  • mosesjact on March 21, 2017, 13:48 GMT

    Knuckleballs will be very effective in cricket if somebody works on it and develops one with good control. The movement in the air is created by boundary layer separation. For that to happen, the ball must not have any spin at all. If the ball spins it loses control and makes it easy for the batsman to handle. If the ball is bowled with the seam pointing at third slip, the ball will swing to the off side but will not spin on the ground. The boundary layer separates early on the off side when air hits the seam and lowers lateral pressure. The same principle can be used to swing the ball towaeds the leg side and also make the ball dip down or float in the air longer. 70 mph is the ideal speed for knuckling. Absense of spin on the ground makes it less effective than traditional spin.

    Rabindra Mehta is an aeronautical engineer who is the best authority on the physics of ball.

  • Paul on March 21, 2017, 9:20 GMT

    Try looking at Stephen Croft of Lancashire when he bowls the first over in T20 games a number of deliveries in those overs are knuckle-balls

  • legnakavon on March 21, 2017, 2:45 GMT

    PYOALB. Fly balls to the outfield in baseball generally carry 100 to 120 yards and are caught. Few carry only 80 to 90 yards.

  • Brett on March 21, 2017, 1:09 GMT

    My mate Mario uses the knuckle ball regularly in our games. He is an ex baseball player, so he is good at it. The ball does not swing particularly more than standard deliveries. He uses it primarily for a slower / variation delivery. Very effective though.

  • Ron on March 20, 2017, 20:49 GMT

    There is, really, no disadvantage placed on any particular team given that the same rules, pitch conditions, boundaries, bat sizes, equipment, etc. are available to both teams.

    I don't understand what the fuss is all about. Fans enjoy watching the ball ricocheting like a rocket off the boundary boards or sailing high into the stands or out of the ground. That is what the game is all about, after all, isn't it, kids?

  • Nandu on March 20, 2017, 15:38 GMT

    Regarding knuckleball - I read about it in the early 80s when reading Dennis Lilllee's 'The Art of Fast Bowling'. Many test cricketers from that era must have tried the knuckleball. As a junior/college Cricketer, I have tried bowling it in the early 80s and got wickets. Every pace bowler should read that book to understand the variety of deliveries you can try.

  • Richard on March 20, 2017, 11:47 GMT

    The Big Bash commentators said Ben Laughlin uses it.

  • Tom on March 20, 2017, 11:33 GMT

    I'd query that no cricketer has tried a knuckle ball. Adam Hollioake used to bowl it. There's a Gloucestershire bowler (whose name escapes me for now!) who was bowling it in the last couple of seasons. And given that the article starts off from that flawed premise...

    The main point, though, is that the aerodynamics of cricket balls and baseballs are fundamentally different due to the different seams, and the fact that the baseball is replaced as soon as it gets the slightest scuff mark on it.

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