In a Test match where 40 wickets fell in the space of 1775 legal deliveries, it's a bit of a conceit to term a non-wicket-taking ball, one that the batsman played with relative comfort off the middle of his bat, the ball of the match, but let's do it anyway.

Day four, second Test, Chepauk. Ishant Sharma to Joe Root, the 35th over of England's second innings. This is the first over of a new spell for Ishant, and he's immediately got the ball to reverse. For the first five balls, it's all inswing. It isn't big, booming, boomeranging inswing, but it's accurate: on a good length, attacking the stumps, with a strong leg-side field to enable that line. Root's defensive technique has to be on point against all five balls, and it is.

The sixth ball is our candidate for ball of the match. Again, Ishant hits the perfect length - it may have drawn other batsmen forward but Root trusts his back-foot game more than most - and this time it reverses the other way. A slow-motion replay reveals all the detail: the shiny side faces outwards, and the seam is canted towards fine leg, like it would be for a conventional inswinger, except it's reversing now and it leaves the right-hand batsman. The ball swings late, starting just before it hits the pitch, and straightens towards the top of off stump.

Root's response confirms what we know already. He is one of the world's top four or five batsmen. He picks the length early, and probably picks the direction of swing early too, noting which way the shiny side is oriented as soon as the ball leaves the bowler's hand. He plays it late, getting right behind what's known in the business as the "second line", and defends towards short extra cover.

No wickets, no runs, and ESPNcricinfo's scorers record the batsman as having been in control. It's a brilliant delivery, but it's an in-between sort of delivery, the sort that doesn't make the highlights packages, not even the longer ones that include plays-and-misses.

Six in-between balls, adding up to one in-between over. These are the bits that go into making a fast bowler world-class. The Ishant Sharma of February 2021, 32 years old and about to play his 100th Test match, is a master of the in-between ball and the in-between over.

A master? Well, you'd have to be that to average 22.91 since the start of 2016. Or 19.34 since the start of 2018 - better than Pat Cummins, better than James Anderson, better than pretty much anyone you can name other than Jason Holder.

For much of his career, of course, Ishant wasn't a master of anything, least of all his own fate. For the longest time, he was, to both his defenders and his detractors, unlucky Ishant. Tall, gangly, with unruly hair, a prominent Adam's apple, an odd, endearing stutter at the finish of his action, and no luck at all. Unlucky Ishant, always bowling good balls and making batsmen look uncomfortable, but seldom actually getting them out.

Split Ishant's 99-Test career into thirds, and you kind of see why he gave this impression. In each 33-Test chunk, batsmen have managed virtually the same control percentage against him, a few decimal points either side of 80. And yet, look at those averages - from Test 34 (Dominica, 2011) to Test 66 (Bengaluru, 2015), he averaged 41.34. Since then, he's averaged 23.42, with barely any change in how often he's drawn uncontrolled responses from batsmen.

So what's changed? Well, two things.

First, Ishant stopped bowling bad balls, and for a time he became India's workhorse: a tireless deliverer of thankless overs, able to control the flow of runs without necessarily looking like he'd run through teams. He did a job for his captains, a job for which he was valued, and through which he became the one unchanging cog in an imperfect attack, the most experienced member of a fast-bowling group that was still finding its way in Test cricket.

On back-to-back tours of South Africa, New Zealand, England and Australia from December 2013 to January 2015, Ishant took 43 wickets in ten Tests at 35.00. Not particularly impressive, you'd think, but only one India bowler managed a better average in that period, and no one had a better strike rate than his 60.8. He also took more five-fors (three) than anyone else.

The second transformation was in the nature of his good balls: they became more potent. He began going wider of the crease to make batsmen play more often, and in doing so rediscovered - according to Bharat Arun, India's bowling coach - the wrist position that allowed him to swing the ball again. He also found a way, with the help of Jason Gillespie at Sussex, to bowl fuller while still hitting the pitch hard.

And he kept getting fitter and stronger, in better shape to maintain his hostility over multiple spells. His action grew smoother, and his body more balanced and stable at the crease, allowing him to bowl with just as much venom from all sorts of angles, turning him into a terror to left-hand batsmen from around the wicket. Just look at him square up Dawid Malan and Ben Stokes here.

In doing all this, Ishant began making his own luck. The good balls did more in the air and off the pitch, but they were also fuller and closer to off stump, just as likely to draw an edge as a play-and-miss. And there were fewer bad balls - from his end and, in a well-deserved turn of luck, the opposite one too - so there were more catchers in place to gobble up the edges. In between came all the pleasing, in-between passages, like the over to Root, where he kept asking difficult questions to good batsmen offering solid responses.

What does it take for a fast bowler to play 100 Test matches? Only ten players have ever done this - 11 if you include Jacques Kallis, who never had to bear a specialist fast bowler's workload - and it's quite a list: Anderson, Glenn McGrath, Courtney Walsh, Stuart Broad, Kapil Dev, Shaun Pollock, Wasim Akram, Makhaya Ntini, Ian Botham, Chaminda Vaas.

That Ishant is about to join those names is a testament to his skill and durability, but it's also vindication for all the selectors, captains and coaches who believed in his ability through his leanest periods. I mean, look at this for a stat:

Of all the players of his age, Ishant makes the best case - Rohit Sharma might be the batting equivalent - for selectors to pick players on potential and back them through thick and thin. In Ishant's case, it helped that India weren't always blessed with a plethora of alternatives in his early years, especially when it came to his particular blend of height, pace, movement and bounce. It also helped that he was prepared to bowl all day, in all sorts of conditions, and to learn and better himself.

In the process, he's overturned the narrative about his career. For a long time, it felt like he was struggling to meet the expectations that had been thrust onto him when he bowled that memorable spell to Ricky Ponting at the WACA as a 19-year-old. You could now say he's exceeded them comfortably.

In a way, Perth 2008 encapsulated everything that made the old Ishant so fascinating and frustrating: he kept beating the bat and kept making a top-class batsman look ungainly, but he wouldn't have gotten Ponting out if he hadn't extended his spell into a ninth over. And that, eventually, was his only wicket of the innings.

Thirteen years on, Ishant is no longer just a towering, back-of-a-length bruiser. In his current avatar, he's close to being the complete fast bowler, streamlined, skillful, and still young enough to make up for all the lean years and end up with a record that truly reflects how much he's grown.

Karthik Krishnaswamy is a senior sub-editor at ESPNcricinfo