Prison Shadows only makes sense in the context of the Thirties and the boxing game. During that decade there were several ring deaths, two of the most prominent were killed by Max Baer in the ring. One was Frankie Campbell who was annihilated by Baer in a match. The second was Ernie Schaaf who took a terrific beating from Baer but survived to be 'knocked out' by Primo Carnera and die after that match. But neither Baer or Carnera served any time for the deaths involved.
As did Eddie Nugent in this film. But he gets a parole and there's a promoter who's willing to back him in the ring as 'Killer Harris'. Apparently that's something no one thought of for OJ in these times. But it's a good gimmick and another fighter dies.
We're never told why someone is doping these fighters to make it look like Nugent has a killer punch. Shades of Primo Carnera. I won't say who, you'll just look at the film and you're never really told why.
This came from an outfit called Puritan Pictures, a poverty row movie company and it shows.