Thursday, 23 July 2015

Does momentum matter?

If there's on thing that we can surely all agree on after the carnage of second Ashes test it's that Australia have "the momentum".

Cricket commentators, and in fact sports commentators in general, really like to talk about momentum. The idea seems to be that if a team scores a win- particularly a big win- in a series they can carry those good vibes with them into the next game, making them materially more likely to win the next one. The defeated team meanwhile, like a mouse transfixed in the path of a charging rhinoceros, better brace themselves for all that momentum coming their way.

I think the frequency with which "momentum" is wheeled out bothers me because it's extremely easy to invoke in hindsight and thereby argue that a particular run of victories or defeats was somehow inevitable, but is very quickly forgotten about when events take a different turn.

So the question for today is: does having the momentum make a difference to the result of test matches?

Specifically I've looked at test series of more than two matches which were poised at 1-1 after two tests. I've chosen to do this because I want to see if the effect exists in games between teams who are fairly evenly matched- otherwise is not an interesting effect at all, it's just another way of saying "Team A is a lot better than Team B and will still be a lot better than them when they play again next week." Moreover, it's the kind of situation where momentum gets brought up a lot.

In a test series poised at 1-1 after two tests, the team which one the second test will be widely proclaimed to have the momentum- having impressively wrestled that momentum from their opponents who won the first test. If momentum helps you win test matches then the team who won the second test should be more likely, on average, to win the third.

So does it work out like this?


After a bit of trawling through the archives I was able to find 59 test series of greater than two matches which were poised at 1-1 after two games. The third test of those series went "with the momentum" 19 times (i.e. the team who won the second test also won the third) but went "against the momentum" 22 times. There were 18 draws. Basically, momentum makes no difference.

If you just look at the Ashes you have 6 with the momentum, 3 against the momentum and 5 draws- which looks better for the momentum camp but is quite likely to be a fluke from the small sample. If you just look at recent test series (last 10 years) things go in the opposite direction, favouring wins against the momentum.

"But hang on," you might say, "Australia didn't just beat England in the third test, they absolutely hammered them- surely that means something momentum-wise?"

Actually, no not really. For the final bit I just looked at those series where the second test was a "thrashing", to see if in those cases the momentum carried over into the third test. Obviously the cut-off for what defines a thrashing is a little arbitrary, but the definition I went with was:

-any innings victory
-any 'runs' victory by greater than 200 runs
-any 'wickets' victory by 9 or 10 wickets

Restricting to that subset the result is: 11 wins with the momentum, 9 wins against the momentum and 4 draws, so still no noticeable effect.

All of this is not to say that Australia won't win the third test. As an England fan I'd like to think they might not, but truthfully, I think they probably will. Before the series began, most observers were saying that Australia had the better side and some people probably revised that conclusion a bit too hastily in the wake of the Cardiff test. If Australia do win at Edgbaston, however, it won't be the momentum that does it for them.

Sunday, 19 July 2015

Does Mitchell Johnson's bowling "feed off" his batting?

One of the subplots as England put the finishing touches on victory in Cardiff was a defiant innings of 77 by Mitchell Johnson. At the time, more than one commentator asserted that this innings would help his bowling, by imparting that most sought after of abstract sporting commodities: "confidence".

Sure enough, in England's first innings at Lord's Mitch caused considerable damage to England, despite the placid pitch, taking 3-53.

So, is this a general pattern in Johnson's career?

I must admit I was sceptical that there would be any evidence for this but it turns out that there is a little bit, but it seems to be a short term effect. By that I mean that when Johnson has a good innings with the bat he often does do well with the ball in the next innings. However, when averaged over the course of a series there is no particular relationship between him batting well and bowling well. 

The short term effect:

Mitchell Johnson has scored 1 century and 11 half-centuries in test cricket. I looked at his performance in the bowling innings immediately following these performances. I excluded the case of his 123* South Africa which was right at the end of a series, so there was no immediately following bowling innings, so that leaves his 11 half centuries.

In these 11 bowling innings following half centuries Mitch has taken 36 wickets at an average 21.33.

Comparing this to his career bowling average of 27.90 it seems that his bowling performance does pick up slightly in the immediate aftermath of a good batting performance.

Over the course of a series:

The graph below plots Mitchell Johnson's bowling average against his batting average for all the completed test series he has played in.
Looking at it by eye there's no clear pattern to associate a good batting average in a series with a good bowling average, suggesting that when averaged over the course of a series Johnson's batting and bowling averages behave more or less independently.

Getting a bit more Mathsy about it, I evaluated Spearman's rank correlation coefficient which is a way of determining how much two datasets are correlated. The answer was pretty close to zero (0.09 if you want to know) suggesting once again that Johnson's series batting and bowling averages are pretty uncorrelated.

So there you have it: the commentators were right- a good innings with the bat does seem to help Mitchell Johnson bowl well next time out. However, if you look at it over a course of a series his batting and bowling averages have pretty little to do with each other.

Monday, 13 July 2015

Shane Watson: LBW magnet, DRS fiend

For my first quick look at the facts behind cricket's stories, I'm going a little bit topical. 

Amongst the fallout of England's surprise victory in the first Ashes test, has been an awful lot of giggling at poor old Shane Watson, his propensity for LBWs and his poor use of the decision review system. Even as he walked to the wicket in the second innings it seemed everyone knew how he would be out and, of course, that he would review it. And so it came to pass.

It occurred to me to wonder if Watto really deserves his reputation as LBW magnet, DRS fiend. Is he really out LBW so very much? And is his use of DRS really so outrageously bad compared to others?

As you can see from the first column in the table, the answer to the first question is a resounding yes. He's gets out LBW an awful lot compared to his teammates in Australia's top seven (Adam Voges isn't included because he's yet to be out LBW in his fledgling test career). Shane Watson has been dismissed in this way a whopping 29 times in his test career- 27% of all his dismissals in tests. A more typical proportion of LBW dismissals seems to be just above 10%, so Shane's 27% really is loads.

No surprises there then. Opposition bowlers aren't idiots, they've been bowling to pin him LBW for a reason and it's been working.

The second column of the table shows for each player how many of their LBWs they could in principal have reviewed, by which I mean that

1)  the dismissal occurred in a match where DRS available to review LBW decisions
2)  Australia had some reviews left at the time
3)  the dismissal wasn't the result of the opposition reviewing a not out decision.

The third column shows how many they actually reviewed and the fourth shows how many they reviewed as a percentage of the 'reviewable' dismissals.

What we see is that while Shane does like a review, his proportion of LBWs that were failed reviews isn't wildly out of kilter with other batsmen in his team. Indeed he's relatively more frugal with reviews than either Michael Clarke or Brad Haddin- who has reviewed every one of his eventual LBWs where he had the option.

In fairness to Haddin, he may reasonably argue that he bats in the last recognised batsman's position at 7 and so he might as well use a review if there's one left to be used. On the other hand, Watson could have made exactly the same argument on Saturday, but it didn't stop everyone finding it very funny.

So, it seems Watson definitely deserves his LBW candidate reputation and that has probably fed in to the DRS fiend narrative- he reviews a lot of LBW decisions because he has a lot of opportunity to! Nevertheless, even if he is a bit trigger happy with the review, he's not the only baggy green to be that way.

Friday, 10 July 2015

The point of this blog

I think it's fair to say that Peter Moores isn't held in very high esteem by most England cricket fans these days. No surprises there- the world cup was a masterclass in sporting incompetence, even by English standards.

As England crashed out of the world cup, poor old Mooresy was widely lampooned for one particular comment, which now seems destined to become his cricketing epitaph:

"We need to look at the data".

This is all very unfair, of course, because apparently he didn't actually say that.

Which is a shame, in my opinion, because people should look at data. Data is great. It helps us to see through the fog of our biases, of the received wisdom of experts and the hyperbole of journalists, to get a glimpse of the world as it actually is.

There's an awful lot of received wisdom in cricket. Just listen to an hour of Test Match Special (just to be clear, I love TMS). You'll be told that one player has a weakness against left arm spin and another scores too many pretty thirties. A batsman has been 'found out' because he's gone three games without a fifty and that a bowler is going to bowl better because he scored runs when batting. You'll hear A LOT about momentum. You won't hear much backing up of claims with evidence.

Some of these things might be true. But I defy anyone who says that they know that, without having looked at some data. Without hard data all of our observations of the world are refracted through the lens of our preconceived ideas. We make our own narrative, but it may have nothing to do with what's really going on.

So I'm going to try and look into these things for myself. I want to take those things which commentators and fans assert as self-evident facts and see if they stand up to the evidence. I'm sure some will pass the test. I'm sure some won't.

Cricket has it's own beauty, which goes beyond what numbers can tell you. But looking at the numbers can give you a fuller picture and a deeper understanding. And in their own way, numbers can be beautiful too.

This is just a fun project for me to learn more about cricket, writing and maths- all of which are things I like. I'll be posting my findings on this blog, we'll see how it goes.