Mohammad Isam is ESPNcricinfo's Bangladesh correspondent. @isam84
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They combined to take five wickets in 108 overs, which doesn't make for good reading, especially when the opposition's fast bowlers have taken 11 wickets in 82 overs. South Africa's fast bowlers took a wicket roughly every 45 balls. Morne Morkel and Kagiso Rabada hurried the Bangladesh batsmen with pace and bounce while the visiting trio couldn't even regularly beat the South African bat.
But amid the wreckage of a performance, Mustafizur offered some promise in the second innings. Coming from around the wicket, he had both Aiden Markram and Hashim Amla caught behind cheaply. Markram, however, wouldn't have been given out had he taken the review. Amla fell trying to guide the ball through third-man. Nonetheless, it was something to hang on to, and Mustafizur provided some sort of a counter.
His change of angle also showed to his fellow pace bowlers that thinking a little out of the way can go a long way in moderately unhelpful conditions. Mustafizur is evidently a very different bowler than Shafiul and Taskin, with his combination of cutters and slower balls, but with teams finding out more about his skills through video footage, it is important for a bowler like Mustafizur to find new ways to get batsmen out.
What he did to Markram and Amla wasn't rocket science. Many left-arm pace bowlers do this to cut down the angle for right-handers to drive freely through the off-side field. In Tests, he has used the changed angle from around the wicket to give effect against right-handers. Six out of his 11 wickets of right-handers have come from bowling around the wicket. In this format, he has already bowled 230 deliveries from around the wicket, which is 39 percent of the 588 deliveries he has bowled to right-handers.
He has used it much less in ODIs though. Only one out of 27 wickets of right-handed batsmen has come from bowling around the wicket. In this format, he has only ever bowled 36 deliveries from around the wicket, which is 6 percent of the 599 deliveries he has bowled to right-handers.
Perhaps he doesn't need to attack the stumps so often in ODIs , which prompts him to bowl so few from this angle. Batsmen are usually hasty in this format so he'd like to angle them away as much as possible, with the hope of finding an edge or deceiving them with his off-cutters.
While he ended up conceding six boundaries from around the wicket, he was more attacking. In Bloemfontein where there is likely to be a more pace-friendly pitch, bowling from around the wicket, particularly if it is on a good length, could create doubt in the batsmen's minds.
Before Potchefstroom, Mustafizur used this angle the most against Sri Lanka in Colombo in March. In an outstanding spell, he removed the in-form Kusal Mendis, Dinesh Chandimal and Dhananjaya de Silva all from around the wicket. On that occasion, he had to create the angle to give the Sri Lankan batsmen something to think about. It ended up being a game-changing spell.
It wasn't as dramatic in Potchefstroom, but it was better than the fourth and fifth stump line used by Taskin and Shafiul. Both these bowlers have looked out of ideas throughout the Test and with Mushfiqur sending out a warning that poor performance will not go unpunished, their days are likely to be numbered. Subashis Roy and Rubel Hossain are in the Test squad, and at least one of them may get the nod.
Taskin's poor form cannot just be blamed on not bowling enough when playing at home. He also lacks in first-class experience - in other words, bowling long spells. He has said in the recent past that bowling in Tests is a new experience for him, and he has also looked lethargic in the field after long spells. While they undergo hard physical training like most Test bowlers, playing experience makes a huge difference.
Morkel was the most experienced pace bowler in Potchefstroom while from Bangladesh's side, it was Shafiul who was playing his 11th Test in seven years. Interestingly, Rabada, who made his Test debut few months after Mustafizur in 2015, has played 21 as opposed to the latter's seven. Taskin and Duanne Olivier both made Test debuts this year but there is a key difference: Olivier has played 64 first-class matches. Taskin has played only ten; both their first-class careers had begun in 2011.