The Angband competition is run by Tony Holmes on a bi-monthly basis and involves downloading a common save file, and playing Angband (or a variant) over the competition period. The first winning save-file wins the competition - and tie breakers and competitions without winners are determined using various parameters: such as deepest unique, highest experience, and so on.
Unlike the Nethack competitions, it involves a degree of trust, because Angband is flexible enough to be downloaded and modified in a large number of ways, and people playing in the competition are not just telnetting onto a central host to play. As the site notes:
The aim of this site is to make the playing of Angband fun by allowing you to play against other *band players.
So it's better to think of the competition as a way of comparing and contrasting one player's Angband experience against other people playing the game, from a common base-line.
The competition has been running since August 2003.