What Is The Real Problem with DRS?

 

 

Ashes 2013

 

HotSpot, Snicko and Ball Tracking

 

October 9^th

 

 

In the interregnum between the two Ashes series that have not been too many hot topics worthy of blogging. However, today an issue has come up that really is interesting as it is one in which the average fan has generally little knowledge of the underlying science and technology.

Today, Channel 9, the broadcaster in Australia, announced that it was removing HotSpot from the technology available to umpires for use in the Decision Review System. The stated reason is cost, but it is not an unexpected decision because HotSpot became controversial after a series of decisions in the summer series. Some of the disputed decisions were due to deficient use of the system, in some HotSpot may have proved unable to detect fine edges, in others there is a suggestion that batsmen may have deliberately set out to neutralise HotSpot. Yesterday Kevin Pietersen was awarded substantial damages for libel after an advertisement suggested that he had used silicone tape on the edge of his bat to supress the HotSpot signal (these damages were donated to charity).

Some fans are expressing indignation that HotSpot, originally sold as “based on science” should be shown to be so unreliable. What is the problem with what appeared to be proven technology and can we actually make it “more accurate” (whatever that means)?

HotSpot works on a sound physical principal that is very simple to understand and, there lies the rub. It is just a thermal imaging camera that detects small temperature variations on the surface of the bat. When the ball touches the edge of the bat friction heats both bat and ball slightly. HotSpot detects this warmth as a bright spot on the image. It is totally infallible, in theory.

Snicko uses the same principal. An impact between bat and ball sets both vibrating, producing sound waves. When the ball takes the edge of the bat, friction produces a vibration that causes a sound that a sensitive stump microphone can detect. An impact between two hard surfaces gives a characteristic, sharp signal, quite unlike the muffled sound when ball hits pad, or the whooshing of a ball whistling past the edge without contact. Again, totally infallible, in theory.

Snicko’s main problem and one that was seen more than once in the Ashes series is that it is extremely difficult to synchronise sound and vision, leading to clear edges being detected when the ball was half a metre past the bat and the bat was nowhere near pad or pitch. In the movie business this synchronisation is done with the famous clapper board that gives a visual image and a clear sound that allow the two to be synchronised with no fuss and bother: Snicko relies on a technician laboriously synchronising two, totally independent feeds, without the clear clapperboard signal to aid him.

Anyone with minimal notions of science – and cricketers, in the main, tend to be a bright bunch, with a high proportion of university-educated players, at least in the United Kingdom – can see how both Snicko and HotSpot can be largely neutralised with a bit of thought. In fact, for at least two seasons it has been well known on the County circuit how to do it. Both systems rely on friction so, if you reduce friction, you reduce the tell-tale signal of a ball taking the edge of the bat.

Rumours were certainly circulating a while back that a good dose of Vaseline on the outside edge of the bat would protect the batsman from very fine edges showing up. Not only would it stop the friction of ball on bat warming the edge of the bat and giving a HotSpot signal, it would also reduce the Snicko signal. However, it does not need to be Vaseline: a well-oiled bat would also be effective (who would think twice about a batsman applying a generous dose of linseed oil on the bat before going out to the middle?) Or, this summer, silicone tape has been the method that it is suggested is being used. It should also said that there is nothing in the laws that stop a batsman applying tape – only the maximum thickness of the covering of the bat and the fact that it should not damage the ball are covered – and batsmen have taped bats innocently as long as cricket has been played; where do you draw the line?

However, HotSpot has two other vulnerabilities that Snicko does not have. As it relies on a warming of the bat, its sensitivity it impacted when conditions are hotter. That is not something that a batsman can influence. The other, most certainly is. HotSpot depends on a localised heat signature and that can be neutralised easily and quite legally. Here is a hint: Dennis Lillee’s famous aluminium bat would have almost immune to HotSpot. If something in the edge of the bat conducts heat away quickly, you can either neutralise the heat signature or, at very least, make it disappear so fast that it would be hard to detect. I am amazed that no batsman, or bat manufacturer, has thought of adding fine copper wires to the covering on the outside edge of the bat. Copper is so highly heat conducting that I would take a reasonable bet that you could make a bat virtually proof against HotSpot detection of edges with it with minimal difficulty and at almost no cost.

The normal reaction to suspicions that a batsman has spoofed a bat against HotSpot is a call for the makers to design a HotSpot that is better and less fallible. This is completely the wrong way to approach it. You can make some improvements by using a larger detectors, with better resolution and higher frame rates and lower noise, you can adjust the bias on a hot day so that a faint signal is better detected, but I seriously doubt that you can improve the sensitivity much: detector technology has improved a long way from the CCDs that I used to use that detected less than a third of incident light and the infrared detectors that had painfully low sensitivity. The detectors that HotSpot uses are direct descendants of the military detectors used to warn of ICBM launches and are pretty much state-of-the-art.

What would make HotSpot more sensitive is to increase the friction from the edge of the bat. Make a stronger signal to detect.

A more sensible approach to HotSpot is thus for the laws to regulate the covering of the bat to make an edge more easy to detect. As most batsmen are happy to use a bat with a protective cover, the simplest way to make HotSpot more reliable is ensure that the covering is standard, at least on the edge of the bat and that it is designed to maximise the HotSpot signature, by increasing friction and ensuring that that the covering is not a good conductor or radiator of heat, so that the signature stays present for long enough to detect clearly. This is not to say that we should start making bats with sandpaper on the edges that will damage the ball. The idea should be simply to ensure that HotSpot gets a fair chance. Any additional covering, lubricants, etc. should be specifically prohibited by the laws. A side effect of giving a better HotSpot signal is to give a better signal for Snicko and a louder audible sound for the umpire. By having the same high-signal covering on both edges of the bat, the chances that an LBW-saving inside edge into the pads will be detected are also maximised.

Strangely, the one element of DRS that a street-wise batsman cannot influence is the one that is normally the most controversial of all. Hawk eye and its ball-tracking competitors are proof against spoofing. The one problem that ball tracking technology has is its application. The point of impact, be it with the pitch or with the pad, is not an issue: when the ball hits the pitch its velocity ceases to be downwards and changes to upwards; when it hits the pad flush on, it ceases to be towards the stumps and changes to away from the stumps; if it hits the pad a glancing blow the ball’s trajectory shows a clear inflection – all these are meat and drink to ball-tracking technology which should be 100% reliable at detecting these velocity changes if the product has been properly designed. The problem is the predictive element and here, at least in part, the sceptics are right.

Let’s take a practical example. The batsman is on the front foot and is hit low on the shin by an over-pitched ball. The point of impact may be two metres in front of the stumps, but the ball may only have travelled 20cm after bouncing. Hawk Eye has to predict where the ball would have gone from just 20cm of flight.

Let us suppose that we are working at 100 frames per second and the bowler is bowling fast medium. After being slowed by air resistance and impact with the pitch the ball is probably travelling at 80-90km/h maximum, say 25m/s, when it hits the pad: we will have just two frames to give us the trajectory of the ball and to extrapolate its flight ten times as far. You can calculate the trajectory with Deep Blue and it will still not give you a reliable answer because you simply do not have enough flight after pitching to know with any confidence where the ball will go.

Now suppose the opposite case: the batsman is on the back foot, 50cm from the stumps and is hit by a ball that has pitched 5m down the wicket – the ball tracking has only to make a tiny extrapolation and if it says that the ball will hit the stumps, you can be as certain as anything on this Earth that it would have hit the stumps.

The problem with Hawk Eye is not that the technology is inherently unreliable, it is that it is, on occasion, being asked to do things that it not capable of doing because it does not have enough information to answer with any accuracy (think of the computer on the Star Ship Enterprise, when it is being asked a question for which there is no answer on available information – it will just reply robotically “insufficient data” and not even Mr. Spock will argue with it).

If you feed Hawk Eye a sensible set of rules, it will give sensible answers: if the batsman is well down the pitch and the ball hits the pad just after bouncing, it cannot give a sensible extrapolation and should tell the Third Umpire that essential fact… NOT OUT! It is just a matter of programming sensible parameters so that if an extrapolation is unreliable, the Third Umpire and the TV viewer are given this information and do not ask the impossible of the system.

One thing that could be programmed into Hawk Eye and that would make it so much easier for officials and fans to understand is to do something that all scientists get drummed into them at school: present the uncertainty in your result! Any trajectory calculated by Hawk Eye will have an error that can also be calculated which, in turn, allows you to calculate a probability that the ball would have hit the stumps. If Hawk Eye tells you that it is 99% certain that the ball would have hit, that should be enough for anyone. If, in contrast, Hawk Eye says that it was just a 50-50 proposition, the batsman should, most certainly, receive the benefit of the very considerable doubt.

As it is, many Umpire’s Call decisions allow the batsman to stay at the wicket when the probability that the ball would have hit was almost certainly well over 90%, which hardly seems fair to the bowler. I particularly recall one case in the recent Ashes where the centre of the ball would have hit under half a centimetre outside the centre of the stump, but the call was “not out” on Umpire’s Call. As the radius of a stump is a minimum of 1.75cm and the radius of the ball is 3.5cm, the ball has to be missing the centre of the stump by a full 5.25cm to avoid hitting, which seemed a bit unlikely in that particular case. If the umpire is uncertain, why not allow him to ask for assistance from Hawk Eye and then just pass a message: “Aleem, 95% chance that that ball was hitting” and let the umpire come to his own conclusion? Let the technology help the umpire, not undermine him, but do it in a way that even the least technologically-minded can see is above board.