Average of Opponents' Buchholz

Average of Opponents' Buchholz, abbreviated AOB, is a tie-break for events in which players do not all face the same field. Buchholz comes first: a participant's Buchholz score is the sum of the final scores of that participant's opponents. It is intended to represent schedule difficulty.

AOB goes one layer deeper. Instead of directly adding your opponents' scores, it takes the Buchholz score of every opponent you actually played over the board and averages those values. Intuitively, it asks not only whether your opponents scored well, but also whether those opponents themselves faced demanding schedules.

The regulations allow ordinary Buchholz or Fore Buchholz, which treats every paired final-round game as a draw for the calculation. The event must state which version it uses. AOB must not be used in a round robin, a format in which every participant plays every other participant, because the field essentially shares the same opposition.

It is different from Average Rating of Opponents, which uses rating values, and Average Tournament Performance Rating of Opponents, which uses how each opponent performed in the event.