P.K. and the Kid (movie, 1987)

P.K. runs away from home because her step-father keeps on harassing her sexually and her mother is ignoring the problem. She hides in the loading space of Kid Kane's pickup, who's on the way to the world championships in arm-wrestling. When he discovers her, he wants to send her home at first, but after he knows the story he takes her with him - and gets himself into big trouble: her step-father is behind them furiously, trying to kidnap her and take revenge for the stress he got from her mother.