Underrated "B" movie about baseball is the HBO movie "Long Gone" with William Pederson, Dermot Mulroney and Virginia Madsen. Also features Lary Riley who was notable as being the baseball playing murder victim in the film version of "A Soldiers Story". It also features William Gibson and Teller (from Penn and Teller) as the owners of the minor league team.
It has substantially a similar plot to "The Natural" combined with "Bull Durham" where you have an aging ball player considering his end-of-career options and a game fixing scheme he needs to play along with. As usual with baseball movies the light wins out over the darkness, because that's baseball man.