find the football match, with a start date less than or equal to 2010-06-21t20:30:00-08:00, where jeong hae sang was an assistant at.
(AND soccer.football_match (AND (JOIN (R soccer.football_referee.assistant_referee_at) m.0c0lq_j) (le time.event.start_date 2010-06-21T20:30:00-08:00^^http://www.w3.org/2001/XMLSchema#dateTime)))