Compute the average salary of the players in the team called 'Boston Red Stockings'.
SELECT avg(T1.salary) FROM salary AS T1 JOIN team AS T2 ON T1.team_id  =  T2.team_id_br WHERE T2.name  = 'Boston Red Stockings'
average salary refers to AVG(salary); players in the team called 'Boston Red Stockings' involves joining tables on team ID and filtering where team name is 'Boston Red Stockings';