The movie came out in 1984. The original copyright on the book is 1952, so it had a good run without the movie around. Malamud may therefore not have been too concerned about a rewrite in the film version. And he passed away in 1986, so probably had other things to occupy his mind when the movie came out. But as a viewer/reader the timing was different for me. I don't believe I ever saw the movie in a theater, but I've watched it a ton of times on TV. Until reading the book, I thought it ranked with Field of Dreams and Bull Durham as the latter day equivalent of It Happens Every Spring, in the sense of lovable fiction that helps baseball fans and fan wannabes renew their passion for the game.
But that is not what the book is about. Roy Hobbs, who is portrayed as a wholesome figure in the movie, he just had horrible luck when he met Harriet Bird on the train, is not really a likeable character in the book, at least not till the very end. He cares about himself and getting what he wants, and that's all. Consider this paragraph from pages 162-63:
The fans dearly loved Roy but Roy did not love the fans. He hadn’t forgotten the dirty treatment they had dished out during the time of his trouble. Often he felt he would like to ram their cheers down their throats. Instead he took it out on the ball, pounding it to a pulp, as if the best way to get even with the fans, the pitchers who had mocked him, and the statisticians who had recorded (forever) the kind and quantity of his failures, was to smash every conceivable record. He was like a hunter stalking a bear, a whale, or maybe the sight of a single fleeing star the way he went after that ball. He gave it no rest (Wonderboy, after its long famine, chopping, chewing, devouring) and was not satisfied unless he lifted it (one eye cocked as he swung) over the roof and spinning toward the horizon. Often, for no accountable reason, he hated the pill, which represented more of himself than he was willing to give away for nothing to whoever found it one dull day in a dirty lot. Sometimes as he watched the ball soar, it seemed to him all circles, and he was mystified at his devotion to hacking at it, for he had never really liked the sight of a circle. They got you nowhere but back to the place you were to begin with, yet here he stood banging them like smoke rings out of Wonderboy and everybody cheered like crazy. The more they cheered the colder he got to them. He couldn’t stop hitting and every hit made him hungry for the next (a doctor said he had no tapeworm but ate like that because he worked so hard), yet he craved no cheers from the slobs in the stands. Only once he momentarily forgave them—when reaching for a fly, he almost cracked into the wall and they gasped their fright and shrieked warnings. After he caught the ball he doffed his cap and they rocked the rafters with their thunder.
Indeed, there is much other darkness in the book, including the fans themselves, particularly the ones who went to see the Knights play before Roy Hobbs was on the scene. And perhaps the worst part, in the book Hobbs takes the money from the Judge. The movie makes him out to be virtuous where in the book he wasn't.
Given these differences, it is odd to read in the book scenes that one remembers from the movie, but where the context is different as a consequence of casting Hobbs' character differently. So I wouldn't call this a great read. It might have been more enjoyable had I not seen the movie before. But then, truthfully, I probably wouldn't have read the book.
Malamud's writing is pretty linear chronologically, not much in the way of flashback, though other characters are curious about Roy's past, while he is unresponsive to their queries. But the Hobbs character goes into frequent reverie. The train ride that starts the book, where he strikes out the Whammer which itself serves as introduction to Harriet Bird, haunts him through the rest of his life. This you can only get in the writing. Movies are not good at getting into the thoughts of the characters, particularly when those characters are not all that verbal.
And there is one puzzle for me. It is minor but I'll mention it here, because I don't understand why Malamud did this. The Knights are substitutes for the NY Giants in that all the other National League teams at the time were mentioned by their real name, including the Brooklyn Dodgers, but there are no Giants. The difference is that Knights were inept until Hobbs arrived. Could Malamud have written the story using the Giants name instead of the Knights? These are the sort of choices novelists make that I'd never be able to master.