Ashwin uses confidence and planning to trap batsmen

It was a sight to warm the hearts of purists. Having disposed of yet another ill-at-ease left-handed batsman from round the wicket, R Ashwin moved over the stumps as Faf du Plessis walked to the crease. Around him the fielders scurried. When du Plessis took guard, this was how they lined up: slip, short leg and leg slip around the bat, backward point, mid-off, two midwickets - one straighter and closer to the bat, the other squarer and deeper - deep backward square leg for the sweep, and a man back at long-on. No one manned the cover region. No cover point, no short extra.

The purists - there must have been a fair sprinkling around the packed stands at the Chinnaswamy - shifted excitedly in their seats. It was the eighth over of an overcast first morning, and India had strengthened their seam attack while opting to bowl on what seemed a damp pitch. And here was their offspinner, inviting a right-handed batsman to drive him through a vast and unmanned cover region.

On TV, commentators often exhort offspinners to try this tactic. Go on, toss it up, invite him to drive against the turn. Plenty of these commentators were former captains who seldom, if ever, tried it themselves - often with good reason, for it is an exceedingly difficult field for most bowlers to bowl to.

It isn't just offspinners who use the gap at cover as bait. Fast bowlers try it too, when the new ball is swinging, encouraging batsmen to drive away from the body and nick to the massed slip cordon. But for many bowlers, that gap is a subconscious deterrent from bowling the fuller length that will encourage those loose drives. Your brain may know exactly where you want to pitch the ball, but your body may still conspire to land it a foot shorter than you want.

Before England's home series against India in 2011, Stuart Broad was facing exactly this conundrum. He was having little success in the 'enforcer' role he had been assigned, which entailed him to use his pace and height to attack batsmen with the short ball, and decided to bowl a fuller length. But the change in approach demanded a change in the stock field he employed.

"I sat down with [the then England coach Andy] Flower and [captain Andrew] Strauss and said, 'Look, I get asked to bowl this bouncer, but I want to be in and around off stump, challenging," Broad told BBC in an exhaustive interview. "So please let me have a cover if we get the chance. I know there are times we'll need three slips, but gully's never really in the game for me. Let me have a cover, and I can try that fuller length.' They said, 'OK, go for it'."

Given the confidence to bowl fuller lengths, Broad was transformed: he picked up 25 wickets at an average of 13.84 as England whitewashed India 4-0.

If a cover fielder helps fast bowlers pitch the ball fuller, he helps an offspinner bowl a wider line outside off. The classic offspinner's dismissal is the right-handed batsman getting bowled through the gate while trying to drive against the turn. While a gap at cover can tempt batsmen into that indiscretion, it can also cause the bowler to shift his line straighter, almost subconsciously, and rule out that mode of dismissal.

Ashwin did not straighten his line. Bowling without a cover to du Plessis, Hashim Amla and AB de Villiers - as good a trio of right-handed batsmen as any in the world today - in the first session of the match, he pitched 19 out of 22 balls outside off stump, nine of which ESPNcricinfo's data team marked as pitching 'wide of off stump'. His length was impeccable. There was nothing overpitched, and the good-length balls spun back enough to deny the batsmen the easy blocked single into the covers. In those 22 balls, he conceded only one run through the off side. With the leg side packed, there were no easy runs to be had while playing with the turn. The pressure was constant.

To be able to bowl as Ashwin did requires perfect rhythm and a high degree of confidence - he definitely had both.

"From Sri Lanka I've not put a cover in place," he said after the day's play in Bangalore. "There have been times when I have been cut through backward point where I've tried to really drop the ball short of the batsman and all that, but even when those runs have gone it's been conscious, it's not like it's fallen in the wrong place.

"But [the gap at cover] gives me a chance to open up the gate, to open my options in the slip region as well, so that way I think it's the confidence and also a bit of planning that goes into not having a cover fielder."

Apart from the confidence to bowl with such a field, you also need to be able to beat batsmen in the air. There is no point tossing the ball up outside off if the batsman knows exactly where the ball will land, and can reach the pitch easily to drive against the turn. In that first session, Ashwin was getting the ball to drop viciously on the South Africans. Du Plessis was a victim of this dip; he looked to step down the pitch, perhaps eyeing the cover gap, and failed to reach the pitch of the ball. Having to change his shot in a hurry, he attempted a leg-side whip - far out in front of his body - and only managed an inside-edge to short leg.

In the space of four balls, Ashwin had taken out Stiaan van Zyl and du Plessis, and South Africa were 15 for 2. In conditions that seemed likely to favour the quicker bowlers, Ashwin's offspin had broken South Africa wide open.

Though he didn't get them out, he kept Amla and de Villiers under constant pressure as well. Sensing that the out-of-form Amla's footwork might not be at its brightest early on, he fired in a few quicker balls to try and hurry him. De Villiers, meanwhile, left his crease frequently, but had to be content with blocking most of his deliveries, with the ball dropping on him and defying his desire to get to the pitch. He saw out the rest of Ashwin's first-session spell cautiously, playing with the turn as far as possible.

Later, there were two more wickets for Ashwin, of JP Duminy and Morne Morkel. The delivery that dismissed Duminy was a beauty, reminiscent of Ashwin's bowling to Kumar Sangakkara during India's recent tour to Sri Lanka. Duminy's step back into the crease suggested he was playing the trajectory - flatter than usual - rather than the length - on the fuller side of a good length - and the ball kicked and turned and hurried the batsman into a nervous poke and an edge to slip: c Rahane b Ashwin.

It is a line in the scorecard that might come to rival 'c Dravid b Kumble', particularly if Ashwin prolongs his mastery over left-handed batsmen. Three of his four victims on Saturday were left-handed batsmen - as are 89 of his 157 in all Tests - but there is growing evidence that he can get on top of the classiest right-handers as well.