Calcutta: Off the field, the most controversial. On it, arguably the most formidable.

That sums up the Chennai Super Kings (CSK), the most successful T20 franchise in India - champions twice both in the IPL and in CLT20.

It's hardly a surprise that at the halfway stage in IPL 2015, the Mahendra Singh Dhoni-captained CSK are topping the table.

After all, CSK have the big guns in batting and bowling, not to mention the role consistently played by Dhoni, India's most successful cricket captain.

Dhoni, in any case, is the type to get more determined when the odds appear to be stacked against him and/ or his team.

That CSK continues to dominate despite the negative publicity because of Narayanswami Srinivasan's conflict of interest issue and his tainted son-in-law Gurunath Meiyappan, is admirable.

The management of Chennai Super Kings Cricket Limited can take some credit for isolating the players from the negativity in the air, but most of it should go to Dhoni.

It probably helps that head coach Stephen Fleming, a highly-rated captain in his time, stays calm just like Dhoni.

"We have a healthy environment, which encourages players to perform to potential. They don't have to worry about matters outside cricket. Their job is to deliver on the field...

"Anything outside the field is the concern only of the management. That's how it should be and we've made that clear repeatedly," franchise director Kasi Viswanathan told The Telegraph.

There has to be something special, or else how would one explain the 'rebirth' of Ashish Nehra, who turned 36 on Wednesday.

Overlooked by the national selectors after the 2011 World Cup, Nehra seems hungry and is perfectly capable of teaching quicks 10 years younger more than a thing or two.

Incidentally, the purple cap (for the maximum wickets in the ongoing IPL), rests on Nehra's head.

"I've dedicated it to my five-year-old son, Aarush," Nehra said, speaking informally to this Reporter.

[The left-armer and wife Rushma also have a daughter, little Aariana, who is half her brother's age.]

Nehra, in fact, has made a mockery of the notion that the T20 format is for the younger quicks. He's the oldest in this edition of the IPL.

"Age appears to be a big thing in India... Look at Brag Hogg, who is 44. Agreed he's a spinner, but hardly anybody talks of his age, probably because he's from overseas," Nehra pointed out.

Hogg is in his first season with the Kolkata Knight Riders.

Asked what kept driving him, Nehra laughed while replying: "The urge to make a difference... I want to keep doing well and I'm really enjoying my cricket."

Has he given up on making an India comeback in one of the shorter formats?

"Selection isn't in my hands. As long as I'm playing, I'm available for selection... In recent years, a whole lot of quicks, except me, have been picked," Nehra answered.

Point made.

Continuity has been a factor and Dhoni, Suresh Raina and Ravichandran Ashwin have worn the CSK colours throughout.

Raina holds the record for the most runs in the IPL (3,498) and for not missing a single match. He's played all 122 of the franchise's games.

Franchises need to be smart at the auctions and CSK were quick to snare Brendon McCullum, by far the most daring captain in international cricket, in 2014.

Actually, at Rs 3.25 crore, McCullum came rather cheap, after being released by the Knight Riders.

It's strange that McCullum has turned out for three franchises in the IPL, when few can match his ability to turn a game on its head.

McCullum's stock was high even before the recent World Cup. It has, since, soared.

Credited with "rebranding" New Zealand cricket, as former captain Ramiz Raja put it, to being hailed as the World Cup's No.1 captain by the iconic Mark Taylor, McCullum has been deserving of every accolade.

McCullum, however, won't be with CSK for much longer in IPL 2015: He'll be required in England for New Zealand's May 8-June 23 tour.

The tour features two Tests, five ODIs and a solitary T20I.

According to Viswanathan, McCullum's last match for CSK will be on May 10, against the Rajasthan Royals.

The last two league games would remain.

McCullum won't be available for New Zealand's tour-opener, on May 8, but will be with his players (in Worcester) ahead of the second match, from May 14.