To your right, you will see the top 5 ranked players for a particular race in NAF tournaments. What does this mean?
Each coach starts with a Coach Rating of 150 for every official Blood Bowl roster. If you attend a NAF sanctioned event using a particular race, your NAF ranking for that race is then activated. When you win a game, you gain Coach Rating. When you lose a game your Coach Rating is reduced. The neat part is that your Coach Rating is adjusted based on the how tough the opponent was. For example, if you lost to a very good coach then you lose less Coach Rating than if you lost to a worse coach. If you play at NAF sanctioned tournaments, then the larger the tournament, the larger the potential change in your CR.
Coach rating is calculated by a complex formula and isn’t for the faint of heart. It’s based on the ELO ranking system. Here is the formula as it stands:
Win Probability = 1/(10^((Opponent’s Rating-Your Rating)/150) + 1)
This probability is then used to recalculate each player’s rating after the match. In the equation below, players receive 1 point if they win the match, 0 if they lose, and 0.5 for a draw. Players’ new ratings are determined as follows
Player’s New Rating = Player’s Old Rating + (K-Value * (Scoring Points – Player’s Win Probability)).
The number of NAF coaches in the tournament determines K-Value in this equation. The formula is:
K-Value = (Square Root (Min(Number of NAF coaches,MAX)) ) * 2
The MAX value is the maximum number of coaches that can contribute to the K-value. The Majors have a MAX of 60 coaches, and are treated as always having 60 if they have fewer, while non-majors have a MAX of 32.