In one of his first "adult" roles (he made his last Andy Hardy vehicle only a year earlier), Mickey Rooney plays Tommy McCoy, a dancer who performs in a going-nowhere nightclub act with his alcoholic father, Brian (James Dunn). Johnny Martin (Mickey Knox), a lightweight boxing champ who is headlining the show that Tommy and his Dad are currently working, admires Tommy's footwork and tells him that he might have a future in the ring. Tommy gives the fight game a try, and he soon proves he's got the goods as a slugger. Before long, Tommy is fighting Johnny for the lightweight title, and after a hard-fought match, Tommy wins -- and Johnny dies. Now dubbed "Killer" McCoy by the press and boxing fans, a distraught Tommy allows his career to be taken over by Jim Caighn (Brian Donlevy), an unscrupulous manager with a gambling problem. Jim drags Tommy through the dirtiest and most dishonest levels of the fight game, but Jim's daughter Sheila (Ann Blyth) sees Tommy's decent side and tries to rescue him. Killer McCoy was a remake of the 1938 Robert Taylor vehicle The Crowd Roars.
by Mark Deming synopsis