Who is the weakest link?

Are Test matches won or lost? The immediate reaction to a match usually focuses on the outstanding performances which can be said to have won it, but I often find it instructive to look at the weakest links which might be said to have lost it. Specifically, I have a hypothesis that you learn most about the difference between two sides by looking at their fourth-best bowlers.

Few substantial Test innings involve less than four bowlers. If you like, they form the four walls surrounding your castle. If the fourth wall is a rickety wooden fence rather than solid brick or concrete, then the cavalry can plunder through and run riot, negating the sturdy resistance being mounted around the rest of the compound. A fourth bowler who restrains batsmen as well as a colander holds soup allows the batting side the luxury of blunting the edge of your best bowlers and just waiting until the runs flow again, whereas a fourth bowler who manages to contain and even take important wickets allows no let-up – which means the batsmen have to take risks against the top men, thus increasing their chances of getting out to them.

At Lord's these last five days, Stuart Broad was England's fourth bowler and Mitchell Johnson Australia's. Broad's match figures were 34-4-127-3 and Johnson's 38.4-4-200-3. Broad's performance was of the not-too-bad variety while Johnson's was somewhere between poor and awful. Since England won, this is an observation of data which confirms the Fourth Bowler Hypothesis (or, to be more rigorous, does not disprove it).

At 23, Broad is still young enough to be classed as a promising up-and-coming player who has not yet mastered his trade, whereas Johnson is 27 and should be approaching his best. Broad's imperfections are therefore more to be expected and offer less cause for major concern than weaknesses in Johnson's game.

England have given try-outs to several young or youngish pace bowlers in recent years: what makes Stuart Broad stand out ahead of most of them is his steady absorption of lessons. On Saturday morning, he ran in and bowled bouncer after bouncer at Nathan Hauritz and Peter Siddle and was treated with as little respect as his poor execution deserved. It was nothing like the chin music with which Fred Flintoff has been serenading Phil Hughes – it was short-pitched dross. Even so, there was a big difference between that spell and the kind of tripe which was served up by the likes of Liam Plunkett, Saj Mahmood and Chris Tremlett: it was deliberate. It may not have been the best of plans and it may not have worked, but at least he was bowling to one. What a captain wants most from any bowler is that he should bowl to the field which has been set, and the best thing about Broad right now is that he is obviously doing his utmost to fulfil that requirement.

Mitchell Johnson, on the other hand, was clearly driving his captain to distraction at Lord's. He was nothing like the electrifying destroyer who had taken South Africa's batsmen apart over the winter. He had no control of length or direction, so his opening spells against Strauss and Cook on Thursday opened the gates of the Australian castle, let down the drawbridge and said “Come on in and pillage our gold.” He it was who allowed England to carry on building momentum after the great Cardiff escape, a momentum which carried England through to victory despite the lack of self-belief which saw them surrender the initiative on Sunday to such an extent that it was easy to imagine Australia setting a record for chasing which would be likely to stand for decades.

This is not an attempt to write Johnson off. Whereas the drop-off in Phil Hughes's performances since South Africa is owing to a weakness being identified and ruthlessly exploited, Johnson's deterioration is purely a loss of form. If or, more likely, when he recovers his composure and control, he will once again be a formidable bowler, but he needs to do so fast if he is not to be dead weight taking up space in the team which could be used far better by someone else in this series.

If the hypothesis is correct, then a comparison of fourth bowlers ought to shine a spotlight on how difficult the respective selectors' jobs are. Broad's problems are not so serious that they cannot be accommodated with the expectation that the experience he gains today will serve him well in years to come, whereas if Johnson continues in this vein he could lose the series for Australia.