Of the first 18 Tests of his career, Ajinkya Rahane had played 17 away and only one at home. For most batsmen that would be an unfavourable ratio - who doesn't like home games, especially at the start of his career? - but for Rahane it worked fairly well, as he notched up hundreds in Australia, New Zealand and England, plus a 96 in South Africa. At the end of that phase, he had a career average of 43.64, thanks to an away mean of 46.37. (The home-away skew is reminiscent of the early careers of Sachin Tendulkar and Sanjay Manjrekar: Tendulkar had 20 away Tests in his first 21, while Manjrekar played only two home Tests in his first 26. Rahane's away average so far is higher than it was for both those batsmen at that point.)

When the home games rolled along thereafter, it did seem early on as if Rahane would help himself to runs in India as well. After a couple of lean Tests against South Africa, he got a hundred in each innings in Delhi, and then made 77 and 188 in the series against New Zealand. At the end of that series, his home average had leaped to 51.75. Combine that with an away average of 51.22 from 21 Tests, and Rahane was shaping up to be the perfect batsman, as comfortable and prolific in overseas conditions as he was at home.

Rahane's home-away stats till Oct 2016
Where Tests Runs Average 100s
 Home  8  621  51.75  3
 Away  21  1588  51.22  5

Over the last 13 months and nine Tests, though, Rahane's home stats have taken a severe beating. While Virat Kohli, Cheteshwar Pujara and KL Rahul have consistently churned out the runs, Rahane's season has nosedived: in his last 16 innings, he has averaged only 25, which is about half of what he averaged going into this period. Among the ten Indian batsmen who have scored 200-plus Test runs since the start of the Test series against England in November 2016, Rahane's average is the lowest.

Indian batsmen in Tests since Nov 1, 2016
Player Mat Runs Ave 100
 V Kohli  10  1047  74.78  4
 KK Nair  6  374  62.33  1
 CA Pujara  11  1017  56.50  3
 KL Rahul  9  717  51.21  1
 J Yadav  4  228  45.60  1
 M Vijay  9  585  39.00  3
 RA Jadeja  11  458  35.23  0
 WP Saha  8  363  33.00  2
 R Ashwin  11  404  25.25  0
 AM Rahane  9  375  25.00  0

After his poor home run over the last year, there is now a huge discrepancy between Rahane's home and away numbers. One of the striking aspects of his home stats is the number of times he has been dismissed cheaply: out of 30 innings, 17 times he has been out below 20, which is a whopping 57%; when playing outside India, that percentage drops to 35 (14 out of 40 innings). Six times in 17 home Tests he has been dismissed under 20 in both innings, the most recent of which were his twin failures in Kolkata against Sri Lanka; in 24 away Tests, this has only happened twice.

Also, while his numbers in India are below par, he hasn't done badly in Sri Lanka, scoring two hundreds and averaging 45.22 in six Tests.

Rahane's home-away stats in all Tests
Where Tests Runs Average <20 scores
 Home  17  996  36.88  17/30
 Away  24  1817  53.44  14/40

Till about a year ago, Rahane's home and away averages were so close that there was hardly anything to choose between the two. Nine poor Test matches later, the gap is 16.55. It is not unusual for batsmen to have such a difference where the home average is greater than the away one, but it is extremely rare for the overseas average to be so much higher. Among batsmen who have played at least 30 innings both home and away (Tests at neutral venues are considered away game for both teams), only three have a higher difference - Mohinder Amarnath, Darren Bravo and Ken Barrington. Among modern batsmen, Graeme Smith is another with a similar difference: he averaged 41.52 at home, and 54.99, a difference of 13.47.

Highest diff between away and home ave (Min 30 inngs home and away)
Batsman Away runs Ave Home runs Ave diff
 Mohinder Amarnath  3008  51.86  1370  30.44  21.42
 Darren Bravo  2167  50.40  1233  29.36  21.04
 Ken Barrington  3459  69.18  3347  50.71  18.47
 Ajinkya Rahane  1817  53.44  996  36.89  16.55
 Wally Hammond  4245  66.33  3004  50.07  16.26
 Alan Knott  2198  42.27  2191  26.72  15.55
 John Reid  2397  38.66  1031  25.15  13.52
 Graeme Smith  5279  54.99  3986  41.52  13.47

Among the 17 Indian players who have batted 20 or more times in the top seven at home since the start of 1990, only one batsman has a poorer average: Nayan Mongia, their wicketkeeper in the 1990s, averaged 27.72 from 34 innings. That Rahane's average is the lowest among specialist batsmen during this period is a telling commentary on how much he has underperformed in home conditions. His middle-order colleagues are at the other end of the table: Kohli is in third place with an average of 56.16, while Pujara is on top, averaging a stellar 62.41.

As you dig deeper into Rahane's numbers against pace and spin, a couple of things stand out. Unlike most subcontinent batsmen, he does better against pace bowlers outside India than in India - the difference in averages is almost 12.

Rahane v pace and spin, home and away
Home/away Pace-runs Outs Ave Spin-runs Outs Ave
 Home  339  9  37.66  657  18  36.50
 Away  988  20  49.40  829  14  59.21

Second, he has especially struggled against legspin and left-arm orthodox bowlers at home, with a combined average of 32.9 against them. Against the same types of bowlers in away Tests, his average is a healthy 68.4.

The bowler who has dismissed him most often in all Tests is Nathan Lyon (six times: three each home and away), while Imran Tahir (twice) and Adil Rashid are the two legspinners who have got his wicket in India, but the left-arm spin stats seem a bit of an anomaly. Among the left-arm spinners who have dismissed him at home are Steve O'Keefe, Zafar Ansari, Dean Elgar, Mitchell Santner, Shakib Al Hasan and Taijul Islam. Rahane's combined average against them is only 34.57, but against Rangana Herath in Sri Lanka - a challenge that you might think would be much greater than against the names mentioned earlier - Rahane has scored 100 off 209 balls, and been dismissed just once. That, in a nutshell, encapsulates his home and away career so far.

Rahane has a couple of home Tests this season to at least partly redress this imbalance in his career numbers, but the good news for him is that there are plenty of overseas Tests coming up for India over the next 18 months. In the immediate context, though, all of India would want Rahane to show some of his prolific overseas form over the next couple of home Tests.

S Rajesh is stats editor of ESPNcricinfo. @rajeshstats.