FOR LOVE OF THE GAME by Michael Shaara (Carroll & Graf: $16.95; 160 pp.). Secret passions can take some bizarre forms, but for the late Michael Shaara, whose 1975 novel about the Civil War won the Pulitzer Prize for fiction, it was a simple, all-encompassing love affair with the game of baseball. In this brief novel, published three years after his death, Shaara bares a soul that worships the game and the men who play it. Billy Chapel, 12 years a major-league star, is one of those engaging "naturals" who always turn out to be more surprised than the fans when they are named to the Baseball Hall of Fame. The story takes the form of the trancelike game that is shaping up as the final one in Chapel's life as age and reflexes begin taking their toll. During the game we flash back to Billy's childhood, the impact of his father on his career and an affair, which, like his body, seems in a stage of collapse.