By Marcus Wilson 16/12/2020


I had the delight of being at Seddon Park on Friday 4 December, watching Kane Williamson on his way to 251 runs. It was a wonderful innings to watch and he’s a perfect example to try to copy if you’re learning to play the game.

Part of his success is down to his ability to defend superbly. He’s able to play the ball really late, to the point that its almost frightening to watch from square on from the wicket: you think the ball has got through his defenses and is about to hit the wicket when suddenly, at the last possible moment, the bat comes down on it and the ball drops harmlessly at his feet. By playing late on it, he ensures the bat is angled backwards so that there is no chance of the ball popping upwards and offering a return catch to the bowler.

But he’s also able to play with ‘soft hands’. That’s a bit harder to explain, but it means that he’s ensuring the defensive shots are not hit hard. In fact (though I’d need a high speed camera to confirm this), I think in many cases the bat is actually moving backwards when the ball hits it, even when he’s playing ‘forward’. The effect of this is that if the ball does find the edge of the bat and heads towards the slip cordon, some of the pace of it has been removed, and it doesn’t carry for the catch. There were a couple of examples of that on the Friday, to the clear frustration of the West Indies bowlers.

In physics terms we can consider the bat on ball situation as roughly an elastic collision – there is little energy lost during the collision. Also, since the bat is much heavier than the ball, we can conveniently think about the collision in the frame of reference of the bat (the centre of mass of the bat – ball system), in other words the ‘bat’s eye view’. To give an example, imagine a straight drive, to a ball doing about 30 m/s (very ‘medium’ pace bowling, 108 km/h). To make things simpler, ignore any angling of the bat – assume it’s absolutely vertical. If the bat is moving forward towards the ball at the moment of impact at 10 m/s, then the incoming speed of the ball relative to the bat is 40 m/s.  (30 + 10).  The ball thus leaves the bat at 40 m/s relative to the bat. Since the bat is moving forward at 10 m/s, this means the ball is now heading back up the pitch towards the bowler at 50 m/s, rather faster than it arrived. In this case, speed has been added to the ball. (There is good reason indeed for considering helmets for umpires and even bowlers.)

Now consider the opposite case. The bat is moving backwards at 10 m/s at the point of impact. In this case, the speed of the ball relative to the bat is just 20 m/s (30 – 10). The ball leaves the bat (towards the bowler) at the speed of 20 m/s relative to the bat. But since the bat is going backwards by 10 m/s, that means the ball is doing 20 ms – 10 m/s = 10 m/s back towards the bowler. The pace has been taken off it – it’s not going to come back for a caught-and-bowled chance.

We can do a similar kind of analysis for balls that are not driven straight back to the bowler (e.g. those that go square of the wicket or take the edge and head towards the slips). Here the analysis is slightly more complicated. Instead of simple arithmetic, such as 30 + 10 = 40 m/s, we need to use vector arithmetic – accounting for the speed AND direction of movement.  That’s not too difficult though. The end effect is similar – if the bat is moving forward quickly, the ball will come away more quickly.  If that bat is moving backwards at the point of impact then the ball will come away more slowly. For the case of an edge, it won’t be that much more slowly, but it may well be sufficient to mean the ball bounces before reaching the waiting slips, as Kane Williamson knows so well.

Of course, it’s one thing knowing this, and one thing to be able to do it.

 

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