The unlucky score in English cricket is 111, thought to be because it looks like a set of stumps. Why this is called Nelson is not immediately obvious but it is said that it is based on the belief that the great Admiral had one arm, one eye and only one of what cricket commentator Brian Johnston called 'the other things'. From what is known of Lord Nelson, the last bit unlikely to be true!
A double Nelson is 222, a triple is 333, and so on.
The unlucky number in Australian cricket is 87 - 13 runs short of a century.