CREATE TABLE table_name_51 (pregame_host VARCHAR, year VARCHAR, play_by_play VARCHAR)

Who was the pregame host before 1992 when there was a play by play of Bob Irving?
SELECT pregame_host FROM table_name_51 WHERE year < 1992 AND play_by_play = "bob irving"
SELECT "pregame_host" FROM "table_name_51" WHERE "bob irving" = "play_by_play" AND "year" < 1992