What is Strength of Schedule?

Strength of schedule is calculated by averaging the win percentages of all opponents a team has played, sometimes including a secondary factor that accounts for the opponents' opponents (second-order SOS). A team whose opponents have a combined .600 win percentage has faced a tougher schedule than a team whose opponents average .400. SOS is important whenever you need to compare teams that have not played the same opponents.

In leagues with divisions or unbalanced schedules, two teams with identical records may have faced very different levels of competition. The team with the harder schedule arguably has the more impressive record. Common uses of SOS include: tiebreaker criterion (the team with the tougher schedule gets the higher seed), power ranking input (combined with win-loss record to produce a more holistic ranking), Swiss system pairings (used to break ties within rounds), and wildcard selection (comparing teams from different divisions).

The main advantage of SOS is that it adds context to raw records. The disadvantage is that it can be difficult for casual fans to understand, and it is somewhat circular: a team's SOS depends on opponents' records, which depend on their opponents' records, and so on. Most implementations use two or three iterations of this recursive calculation and then stop.

League management software can compute SOS automatically and display it alongside standings so participants can see the full picture.