In April 2006, Australian fast bowler Jason Gillespie was sent in as nightwatchman against Bangladesh in Chittagong. The nightwatchman's job is simple and universally understood: survive until close of play, protect the real batsmen from the new ball, and then get out the next morning so someone who can actually bat can have a turn. It is one of cricket's most clearly defined roles. Gillespie apparently didn't get the memo. Or got it, read it, and decided to use it as confetti.
Instead of blocking out a few overs and then getting out the next morning like a normal nightwatchman, Gillespie batted. And batted. And kept batting. He passed 50, and the Australian dressing room exchanged amused glances. He passed 100, and the amused glances turned into bewildered stares. By the time he reached 150, captain Ricky Ponting was reportedly trying to work out how to get his nightwatchman to actually declare so the real batsmen could have a go. Sending messages to a nightwatchman asking him to stop batting is not a situation covered in captaincy manuals.
Gillespie eventually finished on 201 not out — the only double century ever scored by a nightwatchman in Test cricket history. The irony was thick enough to spread on toast: Gillespie had a career batting average of about 18, and this was his one and only Test century (and double century). It was his final series for Australia, and he was dropped after the tour. So Gillespie's last significant act in Test cricket was scoring a double century that nobody expected, nobody asked for, and the captain probably didn't want.
The nightwatchman who was supposed to face 20 balls ended up facing over 400. It remains one of cricket's most gloriously absurd performances.