Roy Bentley, at the time captain of Chelsea Football club and an England international, has a small, uncredited role as an instructor.
Usually reckoned to be the first British film to get an "X" certificate. There were other films before this one that had similar levels of content, and some of those were passed for general viewing. But Cosh Boy was presented for certification just as they introduced the new "X" certificate in 1951. The "X" certificate has since been replaced by the "18" certificate.