How many players debuted their careers from San Francisco 49ers?
SELECT DISTINCT COUNT(?uri) WHERE {?uri <http://dbpedia.org/ontology/debutTeam> <http://dbpedia.org/resource/San_Francisco_49ers>  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Athlete>}
San_Francisco_49ers