He takes the new ball for Pakistan, bowls with his left arm, and swings it into the right-hander. He's a key component of what is arguably the most rounded attack in this T20 World Cup, and how he goes in the powerplay could prove a decisive factor in Pakistan's semi-final against Australia on Thursday.

We could be talking about Shaheen Shah Afridi, but we're not. We're talking, instead, about the bowler Afridi might be if he bowled at 90kph rather than 90mph.

Imad Wasim has played more than 100 games for Pakistan, but cricket is yet to catch up with what he really is. His introduction to the bowling attack continues to be accompanied by TV graphics that describe him as a purveyor of slow left-arm spin, or, even more egregiously, left-arm orthodox.

The left-arm orthodox spinner's stock ball is bowled with the seam pointing to first slip, and is delivered with a mixture of overspin and sidespin. It climbs above the batter's eyeline, then dips, grips, and turns away from the right-hander (watch this over from Bishan Bedi if you prefer things explained visually). There is scant evidence of Imad ever having bowled such a ball in his international career.

Instead, his go-to ball is the arm ball, delivered with his index finger imparting backspin, and with the seam upright and canted towards fine leg. It swings in the air, into the right-hander, and skids off the pitch, hurrying on with its initial angle.

The arm ball is a celebrated part of the fingerspinner's classical repertoire, and Bedi was renowned for it (watch Kim Hughes get his comeuppance), but he probably never bowled six of them in an over, as Imad often does.

Slow left-arm inswing, then, is probably the most accurate label for what Imad does, even if Imran Khan would prefer that you called him a raillu katta - Pakistani slang for a bits-and-pieces player.

And while he might take it to an extreme, Imad represents a widespread tendency among fingerspinners in T20 cricket now. When they bowl to their opposite-hand batter (left-arm spinner to right-hand batter, offspinner to left-hand batter), they predominantly look to bowl balls that go with the angle - usually into the stumps from around the wicket - and only occasionally look to turn the ball away from the bat.

The sliding-with-the-angle ball can be the arm ball or a number of other variations, the most common of which is the undercutter. This is delivered in exactly the same way as the offbreak or the left-arm spinner's away-going ball, but with the wrist cocked back rather than upright at delivery. When the bowler does this, the circle of the seam spins like a slightly tilted frisbee. This produces natural variation, with the ball tending to turn if it lands on the seam, and to skid on with the angle if it lands on the leather.

Mitchell Santner's contest with Virat Kohli in Dubai (ten balls, five runs) was probably the high point of the undercutter at this World Cup. Time after time, Kohli kept looking to make room to hit Santner through the off side. Time after time, the ball drifted in from wide of the crease, and kept going with the angle, often stopping on the pitch too, making Kohli hit too early, with too much bottom hand, towards the bowler or mid-off rather than through the covers as he intended.

No matter what inward-sliding variation the bowler employs, the idea behind it is the same. In white-ball cricket, and in T20 in particular, the batter's most precious resource is room to free their arms, whether to hit with the spin or against it. Denying the batter room can limit their scoring areas drastically.

This becomes particularly important when the spinner bowls in the powerplay, with only two fielders outside the 30-yard circle. Give the batter room and they can hit the ball wherever they please. Cramp them successfully and they're forced to manufacture risky ways of finding the boundary or to be content with singles to the leg-side boundary riders.

Apart from room, the arm ball and undercutter, which lack the overspin of the traditional turning ball, also deny batters the bounce they rely on for lofted hits.

"If anything, it's going to skid on or stay slightly lower, so it's more difficult to get underneath the ball and hit it in the air," says Bazid Khan, the former Pakistan batter who's part of the TV commentary team at the T20 World Cup. "And also, with the arm ball, you can increase your pace and bowl it much flatter or quicker as you like. If you want to turn the ball, and the pitch is not a turner, you can't really bowl into the pitch as quickly as possible and then get it to turn."

At this World Cup, the pitches in the UAE have been on the slower and lower side, which has only made it harder for batters to attack the ball that slides into them.

"A person like Imad Wasim, who's going to predominantly swing the ball into the stumps, on pitches where the ball is not coming onto the bat, it's almost impossible to hit him down the ground, because he bowls it quite quickly and he bowls short of a length," Bazid says.

"When he's bowling in the UAE or on pitches where the ball is not coming onto the bat, where do you risk hitting him? You can't really get to the pitch and hit him down the ground, you can't trust the ball to come onto the bat, and if you go leg-side-ish or if you try to slog-sweep, then you run the risk of getting out lbw, because it's across the line and it's quick, and if you mistime it or if it's a half-hit, you're gone, so it restricts the scoring areas a lot."

That conditions in the UAE have suited Imad's bowling is reflected in his numbers. He has an overall economy rate of 5.23 at this World Cup, and within the powerplay it's a hugely impressive 5.66. Fingerspinners at large have flourished in the tournament. They've conceded a combined 6.61 per over at this World Cup; never before have they been so frugal. And only in 2009 have they returned a better average than their 22.83 in this edition.

They've not been wholly reliant on the pitch either. Where the fast bowlers haven't always found swing with the new ball, spinners have found drift, and genuine swing when they've bowled the arm ball. Even as Australia hunted down 158 in just 16.2 overs against West Indies, for instance, Akeal Hosein went at just 7.25 in his four overs. His prodigiously swinging arm ball followed Aaron Finch as he made attempts to create room for himself, and eventually got him bowled off the inside edge while attempting a late cut.

How have the spinners got the ball drifting and swinging so consistently when the fast bowlers haven't? I put this question to Malolan Rangarajan, the former Tamil Nadu offspinner who's now a talent scout with Royal Challengers Bangalore and assistant coach with CPL champions St Kitts and Nevis Patriots.

"Let's just take one example here, the one-finger [arm] ball, one of the reasons it does swing at times or at least create some sort of an angle, is because of the seam position it has to be released with," Malolan says. "If a fast bowler bowls an outswinger, his seam position doesn't necessarily have to be [tilted towards] first or second slip, but when a spinner bowls an arm ball, the seam position needs to be a little exaggerated at release. That forces the ball to create some sort of angle or movement in the air."

The round-the-wicket angle to the opposite-hand batter also makes it far easier for left-arm spinners to cramp right-hand batters for room, and for offspinners to do the same against left-handers.

"When a left-arm spinner bowls from around the wicket, and he bowls the undercutter or the one-finger ball, even though it starts from outside your eyeline as a batsman, you know that it's ending up towards your body," Malolan says. "The arm comes from so far outside the pitch if the left-armer is bowling from around the wicket, but if a right-arm spinner has to do that, he has to come from around his head."

This, then, is perhaps the biggest reason why left-arm spinners prefer bowling to right-hand batters and offspinners to left-handers. It isn't so much about the ball turning away from the bat as much as the angles that allow the bowler to cramp batters for room.

And bowlers keep finding new ways to do this. R Ashwin, for instance, bowls a reverse carrom ball that's more or less an inswinger to the right-hander (he mostly reserves the traditional arm ball, which goes the other way, for left-handers), and he often jumps wide of the crease while bowling it, to create even more of an inward angle.

"He's got two variants of it," Malolan says. "One swings in in the air and then goes on with the arm, and the other one, which he bowls a lot in the IPL, is he goes wide of the crease, angles it in, and then gets it to straighten. He changes the release a little bit."

If there's been a seeming explosion of drift and slow swing at this World Cup, it may not necessarily be because these skills have been rediscovered, Malolan says. Instead, because wristspin and mystery spin had shunted them to the periphery of T20 cricket for a few years, fingerspinners weren't necessarily getting much of a chance to show off these skills.

"Ashwin for a long time has bowled [the arm ball]. Even the dismissal of Chris Gayle in the 2011 [IPL] final was a one-finger ball," Malolan says. "Shakib Al Hasan still bowls it. I don't know how much domestic cricket you watch, but the number of players who actually do it now is unbelievable.

"Akeal Hosein, we're seeing in the World Cup. He bowls the one-finger ball, he bowls the carrom also. There have been people who do it, it's just that those people haven't been playing. Now suddenly you have these guys bowl in the powerplay and swing it as much as Jimmy Anderson."

As the history of T20 has shown us, styles of bowling keep evolving with time, and as a response to external challenges. While the pitches in the UAE have allowed the inward, cramping angle to flourish, spinners have had to develop other modes of operation on flatter surfaces - the ball spinning away from a wide-ish line outside off stump, for instance, and ending up outside the batter's hitting arc.

In his pomp, Sunil Narine did this beautifully from over the wicket to left-handers - most famously while bowling a Super Over maiden back in 2014. Krunal Pandya takes a leaf out of the fast bowler's death-bowling playbook and uses the wide yorker liberally on flat pitches. And in the 2021 CPL, the Patriots offspinner Jon-Russ Jaggesar mostly went round the wicket against the right-handers, using that angle to exaggerate the away-drift of his undercutters and the away movement of his carrom ball.

Conditions at this World Cup haven't really forced fingerspinners to reach outside the box for these sorts of innovations, though Mark Watt's imaginative use of the crease was one exception. Had the Covid-19 pandemic not forced the tournament to move from India to the UAE, however, we might have seen a little more variety in approaches - or, on the flip side, fewer fingerspinners selected in the first place.

Which brings us to a fascinating question: Imad came into the Pakistan team at a time when they were playing all their home games in the UAE. What kind of a bowler might he have become had his game evolved in Pakistan?

"Pakistan pitches are completely different to how the pitches are in the UAE," Bazid says. "In T20 cricket, whether in PSL or domestic cricket, you're getting scores in excess of 180 as a norm, and in one-day tournaments you're getting scores in excess of 300 and 320.

"We say that pitches in UAE, Pakistan and India are the same, but in actual fact they're not. In India and Pakistan, the ball slides on to the bat in the shorter formats. The outfields are pretty quick as well, and the short ball is coming on to the bat, it's not sticking in the surface, so bowling it short and getting away with it is much harder.

"You'd think that you need different skills there. I think Imad would have developed in the same way, but he might have thought about changing his style a little bit. It may not have been as effective as it has been in the UAE, but then again, the way that he's progressed in white-ball cricket, if Pakistan had played their cricket in Pakistan, who's to say that he wouldn't have developed skills to remain effective?"

Who, indeed. For now, Imad has the chance to make a decisive contribution in potentially two World Cup knockout games. Perhaps he might then emerge from the shadow of his faster and sexier swing-bowling comrade. And maybe, just maybe, he might finally win over his prime minister too.

Karthik Krishnaswamy is a senior sub-editor at ESPNcricinfo