What is the average number of extra runs made as noballs?
noballs refers to Extra_Name = 'noballs' ; average number = divide(sum(Extra_Runs), count(Extra_Runs))
SELECT AVG(T1.Extra_Runs) FROM Extra_Runs AS T1 INNER JOIN Extra_Type AS T2 ON T1.Extra_Type_Id = T2.Extra_Id WHERE T2.Extra_Name = 'noballs'