Going into the tour to Bangladesh in July 2015, Hashim Amla had averaged 66.43 in his last 41 Tests, scoring 16 centuries in just 69 innings - that is a hundred every 4.3 innings. In 15 series during this period (excluding one-off Tests), he averaged 50 or more 11 times, while the average dipped below 30 only twice. In this period of 65 months (February 2010 to Jun 2015), among all batsmen who had batted more than five times in Tests - there were 266 batsmen who made this cut-off - Amla's average of 66.43 was the highest, while only Kumar Sangakkara and Alastair Cook scored more hundreds (17 each).

That period of prolific run-scoring was entirely consistent with Amla's steady improvement as a batsman through this career. After an iffy start in Test cricket - he averaged 33.92 in his first 22 Tests - his numbers steadily improved through each phase: he averaged nearly 50 in his next 19 Tests, before that sustained period of excellence between 2010 and the first half of 2015.

Hashim Amla's Test career Period Tests Runs Average 100s Till Feb '08 22 1289 33.92 3 Mar '08 - Jan '10 19 1482 49.40 4 Feb '10 - Jun '12 18 1693 62.70 7 Jul '12 - Jun '15 23 2293 69.48 9 Jul 2015 onwards 15 766 34.81 2

Since then, though, things have gone pear-shaped for Amla: in his last 15 Tests his average has dropped to 34.81, which is similar to the early years of his Test career. In 22 innings during this period, he has scored only two hundreds. More worryingly, he has struggled to get starts, being dismissed for single-digit scores 10 times in these 22 innings; when he was in his pomp, in the period between February 2010 and June 2015, he had only 12 such scores in 69 innings. From a 17% frequency of such scores (one every 5.75 innings), the percentage has gone up to more than 45 (one every 2.2 innings). Even allowing for the unusually difficult pitches in India in 2015-16, he still has six single-digit scores in 15 innings. In the last year and a half, Amla's contribution to the team's runs has dropped to 14%, down from more than 18% during his best years.

Amla's batting slump Period Inngs Average Inngs per 100 % sub-10 scores % team runs Feb '10 - Jun '15 69 66.43 4.31 17.39 18.22 Jul '15 onwards 22 34.81 11.00 45.45 14.07

Amla's biggest contribution in the South African top order has been his ability to soak up the pressure of an early wicket and make huge scores at No. 3, even when he has come in to bat against the new ball. He averaged 69.48 at No. 3 between February 2010 and June 2015, but in innings when the first wicket fell early, before the score reached 20, Amla averaged 88.07. Some of his highest scores during that period came after South Africa had lost an early wicket; he routinely converted the threat of an early wicket into an opportunity to bat for the longest periods possible. His highest Test score of 311 not out came after South Africa lost Alviro Petersen for a duck in the third over at The Oval in 2012; his second-highest Test score of 253 not out, against India in Nagpur in 2010, came after Ashwell Prince had been dismissed for a duck.

He showed earlier this year that he still hasn't lost that ability, making 201 against England at Newlands after South Africa lost Stiaan van Zyl in the third over, but the failure rate has gone up recently. In the Durban Test against England, Amla made just seven after the fall of an early wicket, and he failed again after an early wicket in Perth and in Adelaide, in the ongoing series in Australia.

The other big difference recently has been his inability to impose himself early in a series: he has averaged 16.12 in the first Test of a series in these last 18 months, scoring just 129 runs from eight innings; six times in these eight innings he has been dismissed before 15, including two ducks. Some of his runs later in the series haven't been as meaningful: his 109 and 96 in Centurion came after England had already sealed the series.

Between 2010 and June 2015, he was at his best in the first match of a series, averaging 85.72 in the first Test (excluding one-off matches), with eight hundreds in 26 innings.

Amla in the first Test of a series Period Inngs Runs Average 100s Ducks Feb '10 to Jun '15 26 1886 85.72 8 0 Jul '15 onwards 8 129 16.12 0 2

Most South African batsmen have suffered a batting slump recently - thanks in large parts to the India series - with only two of their top seven averaging more than 40, but Amla's blip seems more prominent simply because he has been so prolific and consistent for so long. It is inevitable that even the best batsmen have periods when the runs dry up, but Amla's slump has meant his average is in danger of slipping below 50.

Coincidentally, the last time Amla's career average was less than 50 at the end of a Test was after the Adelaide Test of 2012, when he scored 11 and 17, which pulled his career average down from 50.37 before the game, to 49.66 after. That was Amla's 64th Test. Now, after his failure in the first innings of the ongoing Adelaide Test, Amla's career average is currently 50.15. If he is dismissed for fewer than 27 in the second innings, his end-of-Test career average will slip below 50 for the first time in four years. Even if only a temporary blip, it will feel unusual, at the very least, to see a number less than 50 in the averages column next to Amla's name.