Ishant or Umesh - who should replace Siraj in Cape Town?

Among the India seamers who've played at least 10 Tests since the start of 2018, they have the best averages in that period: 21.26 and 21.37.

It's a reflection of India's fast-bowling depth that Umesh Yadav and Ishant Sharma haven't featured in the first two Tests in South Africa, but even as they donned fluorescent bibs and watched their colleagues from afar, they would have known they might be required at some point.

For at least one of them, that moment could come on Tuesday, when the decider begins in Cape Town. Mohammed Siraj may or may not have recovered by then from the hamstring strain he picked up in Johannesburg, and even if he has, India could look to freshen up their pace attack given the physical demands of playing back-to-back-to-back Tests with only three-day gaps (not accounting for the early finish at the Wanderers) between them.

The last time India had such a short gap slotted in between away Tests before this tour was in England, where there was just a three-day gap scheduled between the third and fourth Tests. When the fourth Test began at The Oval, both Ishant and Mohammed Shami were out - Virat Kohli said at the toss that both had "niggles", without going into further detail.

Umesh came in for that Test match, and ended up as India's most successful bowler in a come-from-behind win, picking up three wickets in each innings. It was a performance that showed just how far his bowling has come over the last few years.

Nearly all of Umesh's wickets at The Oval came about via unpredictable behaviour from a more-or-less predictable line. Delivered from the middle of the crease, his stock ball would typically angle inwards and land on or just outside off stump, while swinging away late to hold its line. Every now and again, though, he'd deliver something that came out of his hand looking like that stock outswinger, only with the seam wobbling by accident or design; the ball would end up either following its initial angle or nipping inwards.

Neither the outswinger nor the in-ducker deviated extravagantly, usually, and each magnified the other's threat. Joe Root, in the first innings, played for outswing and left a hint of a gap for the ball to nip back through. Craig Overton, on the final day, played for the initial angle, only for the ball to swing away with extra bounce and square him up to bowl him off the right elbow.

It was the kind of smart, purposeful overseas Test-match performance that had been latent in Umesh for at least three years, but he'd only gotten scattered opportunities to show it. It's hard to prove you're no longer just a home-conditions specialist when you hardly ever play overseas.

Umesh got that chance at The Oval because of the niggles that laid Shami and Ishant low, but it's possible India might have left Ishant out anyway, after he'd endured a rare bad match at Headingley. It wasn't just a bad match in terms of his figures - he went wicketless in England's only innings, while conceding more than four runs an over - but also in terms of his rhythm, with the ball sprayed around as if he'd stepped into a time machine and gone back to 2011.

Ishant's lack of rhythm at Headingley may well have been an outcome of what had been an extended stop-start phase in his career. He had injured his ankle during a Ranji Trophy match in January 2020, and had looked unlikely to make India's tour of New Zealand in late February, only to miraculously play the first Test - and take a five-wicket haul while jetlagged - before missing the second. Then, following a long period of inactivity in the early months of Covid-19, his 2020 IPL season ended early with a side strain, which also caused him to miss India's 2020-21 tour of Australia.

After recovering from that injury, Ishant had played all four home Tests against England - but only bowled 25 overs over the last three Tests, where the spinners did the bulk of the work. Then, in the closing stages of the World Test Championship final against New Zealand in June, he walked off the field after taking a blow to his finger while attempting to stop the ball in his follow-through.

That stop-start phase hasn't gone away. Since Headingley, Ishant has only played one of India's five Tests, against New Zealand in Kanpur. Only those within the team environment will know whether he's regained his rhythm fully or not.

But you only need to go one Test back from Headingley to know how valuable Ishant can be when he's on song. Jasprit Bumrah and Siraj may have delivered the most instantly recallable deliveries of that frenetic final day at Lord's, but Ishant's bowling was just as crucial. He picked up five wickets in the match, and his lbws of Haseeb Hameed and Jonny Bairstow in the second innings broke open England's top order after Hameed and Root had seen out a tense hour of play. Those lbws were typical Ishant 2.0 dismissals: full balls swinging prodigiously into the right-hander.

So who do India go for if they need one of Ishant or Umesh in Cape Town? The answer will depend heavily on conditions. Inconsistent bounce was a massive feature of the first two Tests of the series, and India were significantly disadvantaged in the second Test by a lack of height in their pace attack. Ishant is easily their tallest bowler, but his new-age avatar doesn't necessarily thrive on hitting the deck and getting the ball up to throat height. He's now more of a swing bowler, and, when in rhythm, an accurate throttler of batting line-ups.

This may well suit India's needs, though, given that batters traditionally worry more about sideways movement than bounce in Cape Town. This was certainly the case when India last played there in 2018, when Bhuvneshwar Kumar was their most dangerous bowler, and Vernon Philander was South Africa's match-winner.

So, assuming that both Ishant and Umesh are fit and in rhythm, it could come down to this: do India want a tall swing bowler who can bowl dry when needed, or a skiddy swing bowler who's a little quicker and possibly a little likelier to test both edges of the bat, but could go for runs every now and then?