Question: For which team that has a center did Doug Williams play?
Answer(s):
answer: Washington Redskins

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ns:m.0443ql)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
ns:m.0443ql ns:sports.pro_athlete.teams ?y .
?y ns:sports.sports_team_roster.team ?x .
?x ns:sports.sports_team.roster ?c .
?c ns:sports.sports_team_roster.position ns:m.02_ssl . 
}