McCullum was an exceptionally talented rugby player in his youth was picked in front of All Blacks great Dan Carter at first-five in the South Island secondary schools team in 2000.
The selectors "clearly got it wrong," McCullum quipped in 2014, after he became the first Kiwi to score a triple century.
But Carter has a different view on B-Mac's rugby abilities.
"That year, 2000, he was playing some awesome footy, so I spent a fair bit of time on the bench," Carter has said.
"He was a natural sportsman, good hand-eye."
Those who played rugby with him back believe he could have easily been an All Black.
Luke Tweed was captained by B-Mac in the King's High School First XV.
The underdog high-school team blasted through the Otago Competition and then went on to make the top-four in the national competition. They were then disqualified for fielding an ineligible player.
"I was at the same trials for that South Island secondary schools team and he made the team as the first-choice first-five ahead of Carter," Tweed told Fox Sports Australia.
"I know at the time that was a real big decision for him - to turn his back on rugby and concentrate solely on cricket."
According to The Telegraph even Sir Richard Hadlee was worried about losing McCullum to rugby, with the report suggesting the Kiwi cricket legend asked B-Mac's mates not to lend him any rugby boots.
