It took the umpires to move Ishant Sharma away from the angle.

Just imagine the cost of bowling around the wicket to left-hand batsmen in Southampton last year. This was a pitch beginning to take appreciable turn from the rough. India had an injured spinner in R Ashwin. They were going to bat last. They had nine right-hand batsmen, the ones under real threat from spin because turn was available from only that rough outside the right-hand batsmen's off stump. For left-hand batsmen, the rough fell safely outside the leg stump.

Not only were England's seven left-hand batsmen immune to that rough, India's quicks kept going around the wicket to bowl to them, thus creating more and more rough for Moeen Ali to consign India's right-hand batsmen to doom. The rough was so dramatic that Ashwin even tried bowling over the wicket to aim at the areas outside the leg stump of the left-hand batsmen.

And yet, and yet... it took the umpires to warn Ishant for running on to the danger area to stop him from landing in that rough and making it worse for his own batsmen. What is the pay-off of this angle for right-arm quicks that India were willing to pay such a heavy price for it? Well, big enough, it turns out, to have, over the last five years, in partnership with offspin bowling, neutralised the statistical advantage that left-hand batsmen have enjoyed in Test cricket.

It was an advantage that has become even more significant this century. Mid-2001 is also around the time when ESPNcricinfo began to maintain its ball-by-ball data, which just happens to be a convenient starting point for this comparison. From 2001, till the end of 2014, left-hand batsmen averaged 38.72 in Test cricket, a good six runs per dismissal better than right-hand batsmen. That's a higher advantage than the historical four per dismissal. Since the start of 2015, though, they average 30.5, one run per dismissal fewer than what right-hand batsmen have managed.

One of the factors, of course, is offspin bowling, against which left-hand batsmen average 26.83 since 2015 as against 34.41 before that. While spin bowling is enjoying a general renaissance with the change in the nature of pitches in Asia, the angle has played its part here too. In 14 years before the start of 2015, offspinners bowled two in three balls to left-hand batsmen around the wicket; since then they have bowled nine in ten from that angle.

The shift for fast bowlers has been even bigger, especially given they have a much bigger incentive to bowl over the wicket than offspinners do. Offspinners basically take the lbw out of the equation when they go over the wicket because they only take the ball away: it has to pitch outside leg if it is hitting the stumps, and it has to be missing off if it pitches within. Quick bowlers, though, can swing or seam the ball back in, which becomes more dangerous when it happens against that angle going away. That's why in the past, you would see them use the new swinging ball from over the wicket, and then change the angle once it had stopped moving.

From bowling 18.68% of their deliveries to left-hand batsmen from around the wicket from 2001 to 2014, fast bowlers have bowled 40.3% from around the wicket since. The number went as high as 49% in 2018, the year in which the umpires had to practically drag Ishant away.

What they are trying to do is obvious: cut the room, bring the stumps into play, and get some movement away against the angle in. Nor is it new: the king of this angle, Glenn McGrath, bowled 23.8% of deliveries to left-hand batsmen from around the wicket. Andrew Flintoff operated at 35.98%. The average cost per wicket, though, was better for both of them from over the wicket.

The England coach for a major portion of Flintoff's career, Duncan Fletcher, is known to have encouraged India's fast bowlers to use that angle too. In Fletcher's last Test series as India coach, India's fast bowlers bowled 21.82% of their deliveries to left-hand batsmen from around the wicket, Australia bowled just six deliveries from that angle.

While South Africa might have had brief success with the ploy in 2012 before ditching it, West Indies and England turned this into a long-term tactic in 2015. When England toured the West Indies, their left-hand batsmen faced more than half their deliveries from around the wicket. Stuart Broad, James Anderson and Ben Stokes then repeated the dose to Australia in the Ashes, going around the wicket 41.68% of the time and drawing a superior average of 20.7 as against 53.45 from the more conventional angle.

This was not just a fad waiting to be discovered. It required a certain skill to go with it: apart from the accuracy, most important was the ability to move the ball away from left-hand batsmen. Broad and Stokes do it naturally; Anderson primarily bowled outswing (to the right-hander) but mastered inswing as his career progressed.

Elsewhere, Ishant loved the angle. By 2016, with coach Anil Kumble doubling up as the bowling coach, India's quicks were leading the revolution, bowling 66.84% of their deliveries to left-hand batsmen from around the wicket. There must have been some conviction behind it: they persisted with it despite an average of 37.69 only to reap rewards on overseas tours with averages of 17.38, 22.16 and 18.42 in 2017, 2018 and 2019. India have historically been tortured by left-hand batsmen, but with the natural swing of Ishant and Jasprit Bumrah, the necessary adjustments made by Mohammed Shami, and Ashwin's offspin added to the mix, this team has become a nightmare for them.

Earlier, bowlers went around the wicket when the ball was not moving, but now they are actually benefiting from seam-friendly pitches. It is not too different from Wasim Akram or Mitchell Starc going around the wicket to right-hand batsmen with the reversing ball. Just not as rare. Almost every bowler - Broad, Anderson, Ishant, Bumrah, Shami, Kemar Roach, Shannon Gabriel, Kagiso Rabada - is doing it, and he doesn't need reverse to succeed.

David Warner's struggles against Broad in the ongoing Ashes are a good summation of how difficult it is when a bowler of Broad's quality gets it right: he has fallen to this line of attack all eight times, beaten on the inside edge on four occasions and getting the outside edge on the other four. It is instructive that two of those outside edges came when Warner was actually trying to leave the ball. The seam movement and the angle back in was playing so much on his mind that he was just not able to decide which balls to leave.

This barrage is unlikely to stop anytime soon, and yet the beauty of Test cricket is that two of its all-time great innings have been played in this year and both by left-hand batsmen. How they counter this angle will be fascinating to watch, but one thing is certain: just like their advantage was not permanent, this disadvantage of the left-hand batsmen will not last either.

Sidharth Monga is an assistant editor at ESPNcricinfo