What is the average BMI of all the coaches who have gotten in the Hall of Fame?
average BMI = divide(sum(divide(weight, multiply(height, height))), count(coachID))
SELECT SUM(T1.weight / (T1.height * T1.height)) / COUNT(T1.coachID) FROM Master AS T1 INNER JOIN HOF AS T2 ON T1.hofID = T2.hofID