It All Begins On Opening Day : A Ballpark Figure : SOMETIMES YOU SEE IT COMING: By Kevin Baker (Crown: $20; 326 pp.)

It occurred to me, as I was reading “Sometimes You See It Coming,” that we now possess, unmistakably, a whole strange genre of baseball novel, wherein the hero is some mysterious unknown who comes out of nowhere to become, absolutely, The Greatest Player In The Game. Here, The GPITG is John Barr, who suddenly appears at a minor-league ballpark in some town in West Virginia (which itself disappears later--that is, the whole town disappears) and goes on to glory, although not a scout in all of baseball had ever heard of him.

This theme, of course, was also central to “The Natural,” where Roy Hobbs suddenly materializes with his magic bat Wonderboy as The GPITG, and likewise in “The Year the Yankees Lost the Pennant” (which became the musical “Damn Yankees”) when Shoeless Joe Hardy appears--poof!--in the majors to become The GPITG. Not to mention all the ghostly visitations that come if you will but build it in the cornfield.

One cannot help but muse on this diamond spookiness. It is absolutely weird that everybody keeps writing baseball novels featuring, effectively, aliens. What is it in our national pastime that calls up this impulse?

Well, maybe it all goes back to the person who really was the greatest player (still) in the game. George Herman Ruth went, unknown and unloved, from an orphanage to stardom in the majors virtually overnight--what child is this? the Babe--then on to become the messianic creature who literally saved the game only a few years later. After that truth, apparitional baseball fiction is easy.

Kevin Baker, the author of “Sometimes You See It Coming,” has mined this familiarly bizarre vein nicely, too. He obviously loves baseball and has a knack for telling tall tales, though he also weaves baseball scripture so prominently into the story that good fans who read this book will see a lot of it coming themselves. For starters, John Barr’s antagonist, his manager Charlie Stanzi, is a shamelessly unadulterated copy of the late Billy Martin (right down to his urban cowboy boots), and the ghosts of Branch Rickey, Dick Young, Nippy Jones and Mickey Owen all flutter opaque before us too. Were I to even mention what Hall-of-Famer Barr is identified with at the last, it would give away the ending merely to write the name.

Notwithstanding his famous antecedents, though, John Barr himself is an original, he of the “drowned man eyes” that no pitcher can sneak a ball by. Unfortunately, Barr is not only secretive but so phlegmatic that, by comparison, the character he reminds me most of--Mister Spock--is downright giddy and garrulous. Here, for example, is a sample of the scintillating hero talking:

“ ‘You have a chance to hit over .400,’ Ellie Jay tried.

“ ‘No one’s done that since Ted Williams in 1941.’

“John Barr looked at her.

“ ‘Well? Do you think you can do it?’

“ ‘If I get enough hits.’

“ ‘It’s not a goal then?’

“ ‘Nope.’

“ ‘What is your goal? Another pennant?’

“Barr just shrugged. ‘See the ball,’ he said. ‘And hit it.’ ”

So, give the fact that the main character is, for all intents, mute--just a pair of eyes on the hoof--Bacon has done a masterful job in making us care for him, and wonder about his past and the dark secret that makes John Barr run.

Unfortunately, as the focus of the book is upon a man devoid of personality and of any life away from the diamond (“it was like . . . the ground spit him up every night just for the game”), the author is obliged to fall back on the subsidiary tales of Barr’s teammates on the Mets to advance the narrative. Any author who writes a novel with a hero who plays a team sport must make a choice about how much to write about the teammates. Usually this means diversionary attention paid to the predictable types: the best friend, the clown, the bookish loner, the braggart Lothario, etc. Fill in the the blanks. Here, though, lacking the wherewithal ever to stay with the strong-but-silent Barr for more than a few pages at a clip, Bacon is forced to dwell on the teammates and tell us rather more about them than we care to know.

In a way, even, “Sometimes You Can It Coming” is two quite different, separate but equal novels merged into one. There is John Barr’s mystery, somber and foreboding, on the one hand, and the wacky hi-jinks of manager Stanzi and the Mets on the other. There is, in fact, nary a player on this Mets club who is certifiably sane, and once we get away from Barr, most of the story is downright farcical.

Such drastic tonal juxtaposition as Bacon has created for himself makes for quite a challenge, but he manages somehow to bridge the two companion narratives remarkably skillfully--except, perhaps, with one gratuitous chapter featuring Eileen the Bullpen Queen, which is meant to be bawdy and arch but is instead merely vulgar and cruelly pathetic--and altogether jarring.

Luckily, however, the instant that Eileen mercifully departs the bullpen, we move to the denouement of the novel, staying with John Barr’s story thereafter--a much more satisfying territory than that peopled by his goofy teammates.

By the way, consonant with the book’s mysterious leading man, his creator appears to be every bit as imaginary. “Who is Kevin Baker?” his publishers ask us in a publicity release. Well: “He played little league as a boy. He covered the little league games for the local paper in Rockport, Massachusetts, as a teen-ager. He is the quintessential ‘everyfan.’ ” And that is all. It is apparently not enough that novels about baseball stars who come from the unknown continue to abound. Now, so too apparently will their authors have no prior known existence.