Watch Count Me Out (1938) Official Trailer

Egghead decides his road to riches is through a boxing correspondence course. When he graduates, he takes on champion Biff Stew. Biff pummels him mercilessly (the correspondence course record continues to coach him during the match), but by accident, he knocks Biff out until we see it was all in Egghead's head, after being knocked out by the practice equipment.