How many businesses with the category named Stadiums & Arenas are rated highest?
rated highest refers to MAX(stars); category_name = 'Stadiums & Arenas';
SELECT COUNT(T1.business_id) FROM Business_Categories AS T1 INNER JOIN Categories AS T2 ON T1.category_id = T2.category_id INNER JOIN Business AS T3 ON T1.business_id = T3.business_id WHERE T2.category_name = 'Stadiums & Arenas' AND T3.stars = ( SELECT MAX(stars) FROM Business )