Over a long home season of 13 Test matches, three Indian players played every Test, and each of them made significant contributions right through the season. One of them was Cheteshwar Pujara, who averaged more than 50 in each of the four series, and the other two were the spin duo of R Ashwin and Ravindra Jadeja, whose relentlessness throughout these matches made life miserable for most opposition batsmen.
In 13 Tests, Ashwin and Jadeja took a combined total of 153 wickets, at an average of 24.14. Ashwin's 82 wickets is the most by any bowler in a Test season, while Jadeja's 71 is third on the all-time list. Dale Steyn is the only bowler to come between the two: he took 78 wickets from 12 Tests in 2007-08.
As a combined force, Ashwin and Jadeja were the cornerstone of India's fantastic season: together, they bowled 59% of India's total overs, and took 64% of the wickets taken by India's bowlers. Their poorest combined performance was in Rajkot against England in the drawn Test, when they returned figures of 6 for 363 in 114.3 overs, averaging 60.5 runs per dismissal. In the 12 other Tests in 2016-17, they picked up at least eight wickets between them in every game, and at least 11 in nine Tests. Other than in Rajkot, one of the two always picked up the slack when the other had a relatively poor game. Their best match, in terms of total wickets, was in Mumbai against England, when they had combined figures of 18 for 339. They also had stunning success against New Zealand, picking up 17 in Indore and 16 in Kanpur.
In terms of wickets taken, the tally of 153 for Ashwin and Jadeja is easily the highest by any pair of bowlers in a Test season; the next best is 117, by Glenn McGrath and Stuart MacGill in 1998-99, when the pair played 11 Tests together. McGrath took 63 wickets in those games at an average of 20, while MacGill took 54 at 23. The Australian pair averaged 10.6 wickets per Test, compared to 11.8 for Ashwin and Jadeja, but both pairs took almost exactly the same percentage of their teams' bowler wickets. Unlike this season, in which India played all their Tests at home, Australia played overseas in seven out of those 11 Tests, touring Pakistan and the West Indies, and had a 5-3 win-loss record.
In fact, the list of top eight such bowling pairs in a Test season is dominated by Australia and India - seven of the eight pairs are from these two teams. That's largely because these two teams tend to play more Tests in a season than most other sides: of the 12 instances of a team playing 12 or more Tests in a season, ten are by Australia or India (with one each for New Zealand and South Africa). Also, the list only includes pairs in which each contributor has taken at least 40% of the share of the wickets, to exclude instances of one bowler completely dominating the show. (In the 2007-08 season, for instance, Steyn took 78 wickets from 12 Tests, while the next best for South Africa was 36, by Makhaya Ntini.)
* In Tests where both bowlers played, and where each bowler took at least 40% of the combined wickets
^ % of team's bowler wickets taken by the pair
In the 13 Tests this season, Ashwin and Jadeja had a combined average of 24.14, while the rest of the Indian bowlers collectively took 87 wickets at 35.08, which means Ashwin-Jadeja conceded 10.94 runs fewer per wicket. That's quite a significant difference in average, but there are other pairs who have done even better. In the 1978-79 season, Australia played eight Tests, and in those games Rodney Hogg and Alan Hurst were outstanding, taking a combined 91 wickets at 18.53. The rest of the bowlers were fairly ordinary, though, conceding 39.7 runs per wicket. The difference in average was 21.17, which is the highest between a bowling pair and the rest of the team's attack in a season. Australia lost six of the eight Tests that season, despite the exploits of Hogg and Hurst. (That season was during the Kerry Packer period, when the top Australian players weren't on national duty.)
Among the 30 bowling pairs who have taken a combined total of 75 wickets in a season (with at least 40% of the wickets taken by each bowler), the difference in averages between the Hogg-Hurst combination and the rest of the team's attack is the highest. There are 11 other pairs with a difference greater than the one between Ashwin-Jadeja and the rest of the Indian attack this season, including two by Indian pairs. In 1979-80, Kapil Dev and Dilip Doshi combined to take 109 wickets at 22.74, while the rest of the Indian attack averaged 37.87, a difference of 15.13. In 2004-05, Anil Kumble and Harbhajan Singh jointly averaged 26.19, while the rest averaged 37.79, a difference of 11.59. (Harbhajan missed a couple of Tests that season, so these numbers and comparisons only include the matches where both played.)
Of the 153 wickets that Ashwin and Jadeja took, 95 came when they were bowling in partnership. Ashwin took 56 of his wickets when Jadeja was bowling at the other end, while Jadeja took 39 of his wickets with Ashwin at the other end. Their combined average when bowling in tandem was 21.75, which was about 10% better than when not bowling with each other. That could also be because they would have bowled together when conditions were more favourable for spinners, but all of these numbers point to a season of unprecedented success for the two Indian spin stalwarts.