Cricket, tennis and now football use Hawk-Eye - but how accurate is it?

Hawk-Eye's technology is an impressive tool that makes the lives of referees and umpires easier, but don't be fooled - there's a chance that Hawk-Eye could sometimes get a call wrong.

Hawk-Eye is a device used to reconstruct the track of the ball for LBW decisions in cricket and for line calls in tennis. It will be much in evidence during the remaining Ashes tests and is now being used for goal-line decisions in Premier League football. The technology is at its best when officials make a really bad decision.

But there are things you might not know about Hawk-Eye. For instance, it cannot track the ball to a millimetre even though one might get this impression when watching some replays; in tennis, those shots shown to be touching the line by a hair’s breadth and called in might actually be out and vice-versa.

Few people realised that there was an issue with accuracy until my colleagues and I wrote about it in 2008; even top scientists were quite surprised until they thought about it.

How it works
Reconstructed track-devices such as Hawk-Eye work by using a number of TV cameras to record the position of the ball in each frame, then a computer reconstructs the path and projects it forward from the last frame.

These devices were first used to aid leg-before-wicket decisions in cricket. The projection-forward principle is the same in tennis since it is unlikely that a camera shutter will be open at the exact moment the ball hits the ground next to the line so the crucial position has to be estimated from a series of previous positions.

What we uncovered
From the frame-rate of the cameras and the speed of the ball, a back-of-an envelope calculation gave the range of possible accuracy and it turned out to be less than the replays suggested. So we telephoned the firm to talk about it and we hit a wall. As sociologists of science we had spent decades chatting with scientists about this kind of thing but suddenly we were told this information was private and lawyers were on call. Before we could publish our first paper we had to ask Cardiff University to back us in case we were hauled into court.

Our results were based on the range of possibilities for frame-rate and such other technical matters we could glean from the internet but detailed data for these devices was and still is secret. The International Tennis Federation refuses to release the details of its tests and the International Cricket Council also keeps its results under wraps. I have tried and tried to get the information from them and the scientists they commissioned to do the testing but am always met with the claim that the information is commercially sensitive.

Margin of error
The problem with reconstructed track devices is that their output is based on estimates. The position of the ball in any one frame is a blob of pixels. The future path of the ball must be extrapolated from at least three frames if the ball is swerving but if it is moving fast and the bounce point is near to the crucial impact point there may not be three frames.

Even with three frames, projections have errors and if, as in tennis, the ball distorts on impact, the footprint on which the line call is based is, again, the result of an inexact calculation – and so on. Hawk-Eye itself used to claim an average error of 3.6 millimetres; more recently it claims this has been improved to average of 2.2mms. However, particularly in tennis, the reliance on this technology to provide a definitive call means that this margin of error isn’t reflected in the replays, leading most fans to assume it is 100 percent accurate.

Accuracy, of course, will depend on the speed and the angle of the ball and many other factors which is why these are average figures and, as with all averages, on occasion the error will be bigger – sometimes much bigger. To know what is going on one needs details of the tests and the distribution of errors that resulted.

Tech and circuses
Assuming that tennis and football lovers, unlike enthusiasts for, say, the professional wrestling circus, want to see fairness as well as an entertaining spectacle, they ought to know more about how the technology is trying to work out what happened to the ball.

When the ball is really close to the line we should see something like a spinning coin to indicate that the final judgement has a lot of chance in it. The crowd would still get its decision and fun but something closer to the truth would be on display.

More and more, computers are able to simulate what looks like reality and this is dangerous for the future of society. The public needs to learn to question technological claims such as those that have been made for anti-missile weapons systems. In certain sports some spectators think that technology is infallible when it is not.

Paul Hawkins, the founder of the Hawk-Eye company, recently said our arguments were “typical of people who spent a lot of time in universities rather than on the tennis circuit”. He’s right, and thank goodness for that.

Harry Collins does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.The Conversation

This article was originally published at The Conversation. Read the original article.

 

The Conversation

Andy Murray reacting to a Hawk-Eye call at Wimbledon, 2013. (Photo: Getty)
Getty
Show Hide image

Former Home Secretary Jacqui Smith: Theresa May is the Tory leader Labour should fear

George Osborne is not inevitable as the next Tory leader – and Theresa May could be the one to see him off.

Some people believe that Theresa May has had her day as a Tory leadership contender, but she is a woman who has been underestimated throughout her career. Furthermore, as Angela Merkel, Tessa Jowell, Margaret Hodge and Harriet Harman will tell you, we are in the day of the (slightly) older woman politician. And, while Margaret Thatcher was certainly not an advocate for more Tory women, her legacy is a Conservative party who would not find it impossible to countenance another woman in charge. Could that be May?

Throughout her political career, May has never been seen as “a rising star”. She was involved in politics at Oxford University having gained a place from her grammar school, but was not particularly pushy or sparkling future leader material. She worked in banking for a period and was a councillor in Merton. She fought two unwinnable seats before finally getting elected to parliament in 1997. So no easy, gilded rise through the party for her. Being on the receiving end of some of the misogyny found in all parties’ selection procedures may have been the spur which led her to declare the Conservatives the “nasty party” in her famous 2002 conference speech as party chair under Iain Duncan Smith’s leadership. She is a bit of an outsider, willing to argue that her party had to change and to reach out beyond its natural supporters. She is no Robert Halfon-style, blue-collar Conservative, but nor is she a “posh boy” – perhaps the perfect positioning for a future leader.

Thatcher prided herself on being an ‘honorary man’ – no feminist solidarity for her. However, May is much more comfortable supporting other women – she is an advocate of the Tory party’s efforts to find more women candidates. As party leader, she might well find ways to appeal to the older women who tend to vote, but have not always been attracted by the “calm down, dear” machismo of the current  Tory leadership.

A winning party leader will have to command the political centre-ground. May is no rightwing ideologue. She shows little passion for eye-catching policy announcements and has rarely, in recent years ventured beyond her Home Office brief to express strong views or a sense of the direction she would like to take the country in. The British public may not be attracted by demagoguery, but they will need a clear idea of what a May leadership would believe in and do. This could be an even greater barrier to actually getting elected within the Conservative party to begin with. For example, May has largely avoided the issue of Europe. She did make a speech last year criticising the stifling effect of European Union regulation, but the context was interesting. Some saw this as an attempt to broaden her appeal within the party, but it was also made at the time when she was attempting to win support to opt back in to a range of EU justice and home affairs measures including the European arrest warrant, which the government had opted out of in a grandstanding gesture. She may have to make ideological gestures to win  Tory support, but is fundamentally pragmatic.

However, that is not to say that she is not willing to be brave in taking on those who she feels need challenge. Her “nasty party” speech was one such example, but more recently she was willing to offer some home truths to the Police Federation at its conference. This was certainly at a time when the Fed was already weakened by internal divisions and the police was dogged by scandal. But, as any Home Secretary knows, the conference can be an unpleasant and surly event and it shows mettle to take them on in this arena.

Her time as one of the longest serving home secretaries is a double-edged sword for an aspiring Conservative leader. Being Home Secretary is a serious and difficult job – holding onto it for as long as she has means that nobody could doubt her credentials to take one more step up the ladder. Dealing with the security, cross-government issues and “events” which are the bread and butter of Home Secretaries is possibly a better qualification to be Prime  Minister than the more controlled environment of the Treasury. However, the all-encompassing seriousness of the role also makes it more difficult to win support as a future leader or prime minister. Being Home Secretary with the current policy portfolio is essentially about stopping bad things from happening. It does not leave a lot of time to make the wider political arguments or to engage in the “hopey, changey’” thing which many would look for in a future leader.

She has made mistakes – alienating the civil service in a particularly cavalier shifting of the blame onto senior Border Force official Brodie Clark for supposed weaknesses in border security when the fault was in her policy decisions. She has shown bad judgement and a lack of imagination in sticking with a crude immigration cap which achieves the double whammy of being impossible to deliver and perverse in the impact of trying to.

There is no doubt that May is not a clubbable or particularly warm person so has not built up a cadre of enthusiastic supporters. She has lost some good ministers from the Home Office, like Nick Herbert and Pauline Neville-Jones, suggesting that she may not excel at building the sort of team spirit needed to win a leadership bid and maintain the ‘machine’ necessary to be a successful leader.

However, she has built her career so far on not being a “natural” for each of the political jobs she has held. She has outperformed expectations and has some of the ingredients necessary to move the Tory party on from the dilettante gentleman, amateur approach of David Cameron. It is a record and an approach which just might attract both the party and those voters who Labour so desperately needs to win back. Don’t write her off yet.

This essay is from Face-Off, a series of linked articles by Progress on the next Conservative leader.