The mystery of the knuckleball

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.

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.