SELECT min(T2.HS) ,   T1.pPos FROM tryout AS T1 JOIN player AS T2 ON T1.pID  =  T2.pID GROUP BY T1.pPos
What is minimum hours of the students playing in different position?
[Schema (values) (types)]: | soccer_2 |  College : cname (text) , state (text) , enr (text) | Player : pid (text) , pname (text) , ycard (text) , hs (number) | Tryout : pid (text) , cname (text) , ppos (text) , decision (number);