Just why is Brendon McCullum retiring, again?

The New Zealand skipper wrote his way into the record books with an incredible assault on Australia in the first day of the second Test against Australia in Christchurch on Saturday. It was a fairytale finish that could not have been scripted better - in his last outing in international colours, McCullum rewrote the record books, scoring the fastest-ever century in Test cricket. His century came in only 54 balls, overtaking West Indian great Viv Richards and Pakistani captain Misbah-ul-Haq who had taken 56 balls to reach the target.

When he came in, New Zealand were 32/3 in 20 overs. But over the next few hours, "Baz" unleashed mayhem. At times, he did get lucky, with edges flying over the keeper and when he was 39, he was caught off a no-ball. But fortune undoubtedly favours the brave and he continued on his merry run, stepping out to the bowlers and smashing everything in sight.

When he finally departed on 145 off just 79 balls, New Zealand were 253/5. While McCullum was at the crease, they had scored 221 runs in just 25.3 overs, a run-rate not out of place in the Twenty20 format. Yet again, McCullum had demonstrated that he could change the course of a game in just a matter of hours. The only depressing bit? We have probably seen him for the last time in international colours.