It's as close as cricket gets to a death sentence. If Glenn McGrath announces you as his target before a series, you know you're living on borrowed time. Having stamped cockroach Atherton into retirement and inflicted mortality on Brian Lara, McGrath decided Gary Kirsten was his target in the recent Australia-South Africa series. And true to form, McGrath nailed Kirsten in the tone-setting first innings of all three Tests. Before his defiant 153 in the last Test at Sydney, Kirsten had never scored more than 55 in 17 South African defeats - not quite a case of if he fails, South Africa lose, but definitely a case of if South Africa lose, he's failed. Jacques Kallis may be the class act in the South African batting order, but Kirsten is the glue.

Throughout his career McGrath has had an outstanding record against left-handers. Five of his ten most frequent Test victims are southpaws, a list that includes Lara and Kirsten, and much of that is due to his success bowling around the wicket. In this series he bowled almost 65% of his deliveries to Kirsten from around the wicket, and the stats show why.

Kirsten was in control of all 40 deliveries he faced from over the wicket, but when McGrath switched he was able to produce 17% uncontrolled shots - that's edges, play-and-misses, or any shot the batsman is not entirely in control of - including all three dismissals.

As well as being more likely to lose his wicket, Kirsten was a lot less productive when McGrath went around the wicket: he made 26 runs off 74 balls as opposed to 20 off 40 from over the wicket, a difference of almost one run every over.

That had much to do with the line McGrath bowled. As the below graph shows, when he came over the wicket the angle from which he bowled meant he was much more likely to pitch it on or around middle stump, and Kirsten was able to either work the ball off his legs or drive through the off side.

But when McGrath switched to around the wicket he was able to probe relentlessly outside off stump - when he bowled over the wicket only 28% of his deliveries pitched outside off (11 out of 40); from around the wicket it was 83% (62 out of 74), almost three times as many. The difference in the angle meant that as well as giving Kirsten nothing to work to leg, McGrath knew he needed only a small amount of seam movement to punish any lack of patience from Kirsten. Twice he was thus rewarded: in the second Test Kirsten inside-edged onto his stumps, and in the third he was caught in the cordon fencing outside off.

McGrath's length was also crucial to his mastery of Kirsten. Our study of Kirsten's innings at Sydney shows just how dangerous he is if you overpitch, but as the graph shows, only 7% of McGrath's balls to Kirsten were of full length (8 of 114). Ironically one of those deliveries was the full toss at Adelaide which slipped out and trapped Kirsten lbw.

When McGrath bowled a full length Kirsten scored at 9.00 runs per over (12 runs off 8 balls), on a good length at 2.15 per over (28 off 78), and short of a length - a perfect McGrath length, off which he is close to unhittable - just 1.29 per over (6 off 28).

When McGrath went round the wicket, those figures were even more pronounced: full 8.4 per over (7 off 5); good length 1.96 (17 off 52) and short 0.71 runs per over (2 off 17). In the crash-bang-wallop world of contemporary Test cricket people have less time for the old-fashioned values of building pressure, but McGrath does it as well as anyone and it's easy to see why he's so successful.

Rob Smyth is on the staff of Wisden.com.

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