What is the average weight of the players who have won the award of Rookie of the year?
"Rookie of the Year" is the award; average weight = Divide (Sum(weight), Count(playerID))
SELECT AVG(T1.weight) FROM players AS T1 INNER JOIN awards_players AS T2 ON T1.playerID = T2.playerID WHERE T2.award = 'Rookie of the Year'