Often the chatter from behind the stumps in a cricket match is inane babble. The 'keeper and slips are often just talking to keep the batsmen under pressure, or to encourage the bowler. But sometimes they say things that are quite revealing.
The most interesting thing I heard was from Adam Parore, to a young Daniel Vettori, just after Vettori had spun one past the edge of a batsman. It was something along the lines of "that was a good TV ball, now spin one less and actually get him out."
The concept of a spinner trying to spin the ball less was a strange one.
Mitchell Santner's thirteenth delivery in the match against Bangladesh was only his second ball that appreciably moved off the pitch. And yet he had only conceded two runs in those overs. The pressure he'd created also brought about a run-out.
Mitchell Santner, a spinner, had created pressure without spinning the ball. He mostly did it through the two other weapons of a spin bowler: flight and drift.
Drift is when spin on the ball causes the ball to swerve through the air. In physics, it's known as the Magnus effect. A ball that is spinning so that it will go to the left after pitching will drift to the right, and vice-versa.
The effect is most pronounced in terms of sideways movement if the plane of rotation is perpendicular to the direction that the ball is travelling. The squarer the ball is, the more it will drift. But that also increases the chance of the ball skidding off the surface and not spinning at all.
With Santner bowling left-arm orthodox from around the wicket to a right-hander, the standard drift is into the batsman, like an inswinger. By adjusting the angle of rotation he can adjust whether or not it drifts.
The variation in drift accounted for some of the pressure on the batsmen that Santner created, but his flight was a bigger factor.
Flight is a term that incorporates three separate things: trajectory, pace, and dip.
It is quite possible for a ball that comes out of the hand on an initial trajectory to go towards a batsman's head, knees and one that's aimed over his head, to all land on a good length just by adjusting the pace. Quicker balls won't drop as much as slower ones, so aiming a bit higher, but releasing the ball a bit slower will cause it to land on the same length.
That is a fairly easy concept, but the complication comes with the third component — dip. Dip is caused by the Magnus effect, similar to drift, but rather than the ball moving sideways it either drops faster or slower (depending on the spin direction) than a ball that wasn't spinning.
Some common ways of changing this for a finger spinner can come from bowling "over the ball" or "under the ball." Nathan Lyon is an example of an "over the ball" spinner — when he releases the ball he runs his fingers down from the top of the ball, imparting some top spin as well as side spin. This means that the ball dips more, and bounces higher. Ravindra Jadeja, however, does the opposite. He predominantly bowls "under the ball", having the backs of his fingers facing the ground at the point of release. This imparts a degree of backspin, that causes the ball to bounce slightly later than the batsman expects, and keep a bit low.
As a result, Lyon is more likely to get batsmen out caught, while Jadeja gets a higher proportion of his wickets bowled or lbw.
Initially, spin bowlers varied their flight mostly to be able to allow themselves to bowl slow enough to get the ball to turn. There are four main factors that go into determining if, and how much a ball turns: the speed of rotation, the velocity of the ball, the angle of spin and the nature of the pitch. The velocity, rotation speed and angle of spin can be combined to create a ratio between surface spin speed (at the point that hits the ground) and velocity of travel. Each different pitch has a ratio point where the ball will start to turn. The higher above that, the more it will turn.
If you bowl slowly enough, with enough spin, it is possible to get a ball to spin on glass — but no batsman is going to wait for a ball that slow to bounce. That's part of why the spinners tend to spin the ball further in junior cricket than in senior cricket. The batsmen are less capable of coming down, and so the spinners don't need to bowl at the same pace.
But extra pace isn't the only way to beat a batsman. Variations in flight can do it too.
Variations in flight (trajectory, pace, and dip) can make a huge difference to how the ball gets from the hand of the bowler to the batsman, without relying on the pitch to turn at all.
In New Zealand's match against Bangladesh, it was varying these things that made Santner so difficult to play. He varied his pace by about 40% (from slowest to fastest). He bowled some flat and looped some up, and a range of different trajectories in between. He visited a few with various different angles and amounts of spin so some dipped, some drifted, some did both and some did neither.
Rather than relying on the pitch to assist him, he almost took it out of the equation. The few balls that did turn off the pitch were a bonus, rather than a requirement for his effectiveness.
The team that wins this World Cup will probably have their spinner(s) make a big impact. It might be the wrist spinners deceiving the batsmen off the pitch. But if the pitch conditions aren't as useful, it might be the more subtle skills of the finger spinners, using flight and drift to beat the batsmen. And if that's what is called for, New Zealand have an ace with Santner.