NOBODY UNDERSTANDS baseball. Our national pastime is one part business, two parts sport, three parts ritual, and four parts myth. Does that add up to 10? Who cares? Those of us who love the game know that it wasn't designed to be understood. It was designed to be talked about.

Nobody loves baseball more or talks about it better than Thomas Boswell. How Life Imitates the World Series is the richest, savviest, most pungent baseball book to come along in years. It's laded with enough talk to make you wonder if Boswell's muse is Casey Stengel. Many of the articles in the book first appeared in The Washington Post or Inside Sports, where baseball aficionados promptly recognized them as classics. And now that they're all between covers, Boswell can claim his rightful place with Ring Lardner, Red Smith, Roger Angell, and the other celebrated interpreters of the game. He is one of baseball's bards.

He's not always an elegant stylist, but why should he be? Baseball is not always an elegant game. (Remember the Phillies-Astros playoffs in 1980? Boswell describes that unforgettable farce as "something out of a hookah dream.") Baseball's moods and rhythms, its colors and textures, change as unpredictably as the weather. Boswell is a good enough writer to catch them all. He can be lyrical, somber, elegiac, ebullient--but he always has a wisecrack ready when he needs it. If baseball is mostly talk, the wisecrack is the form of talk that the game has refined till it approaches the condition of art.

One Boswell phrase that has stood the test of time is "sacrifice thigh." Most fans will remember how Mr. October, Reggie Jackson, broke up a Dodger double play in the 1978 World Series. On his way from first to second, Jackson interposed his leg; the throw hit him, the ball dribbled into the outfield, and the runner was safe at first. Sacrifice thigh. Perfect.

This book cackles with puns and epithets. Boswell dubs Steve Carlton, the enigmatic Phillies pitcher who refuses to speak to the press, the Sphinx of the Schuylkill, a.k.a. the Dark Lord. And who but Boswell could write an article called "Glove's Labor Lost"? Or refer to Reggie Jackson as baseball's "Hester Prynne . . . with a dollar sign on his chest"? Or describe the face-off between Goose Gossage, the well- known "prehistoric" relief pitcher, and George Brett, the best hitter in the game, like this:

"The confrontation . . . lasted only one pitch. Gossage's best murderball came in at light speed and Brett sent it out at Warp Factor 1. Make the jump to hyperspace, Wookie."

This is the same writer who quotes Yeats, Keats, and Emily Dickinson with the greatest of ease; who remarks, apropos of the beisbol fanaticos sipping hot tea in the blazing heat of Cuba, that "baseball is thought to be sufficient inebriation for any Cuban"; who explains the jinx of the Red Sox, a team with a long and haunted history, as proof that "Those who cannot forget the past are also condemned to repeat it."

Boswell's profiles of the greats--Jackson, Brett, Carlton, Pete Rose, Ron Guidry, Thurman Munson, Ted Williams--are tactful without being toadying. He lets the men speak for themselves as much as possible, and he listens to what their teammates have to say about them--talk, talk, and more talk, so much of it that reading the profiles can seem like eavesdropping in the clubhouse. It has the savor of authenticity. And readers who like to think of baseball players as dummies are in for a surprise--these guys may have a plug of tobacco in their cheek but they are articulate.

Boswell has a special talent for the subtleties of the game, the nuances of strategy and tactics that make the difference between victory and defeat. He chronicles campaigns and individual games with as much passion for detail as a military historian. He subscribes to the Big Bang Theory: "Baseball is a game of big innings. In a majority of games, the winning team scores more runs in one inning than the loser does in nine innings." Simple enough, but Earl Weaver, the Bismarck of baseball, is one of the only managers who knows how to apply it. Weaver's Orioles have won more games year in and year out than any other team in baseball.

The Big Bang Theory is one of the "conceptual jimmies" that Boswell uses to unlock the secrets of the game; Total Average is another. This statistic, Boswell's own invention, is a measure of a player's total offensive output. Each base that a player produces, including walks and stolen bases, is added; the total bases are then divided by total outs. Thus, Brett's Total Average in 1980 was a phenomenal 1.278, meaning that Brett produced more bases than outs. Only three players besides Brett cracked the 1.000 mark that season--Mike Schmidt, Reggie Jackson, and Rickie Henderson. Only 17 players in the history of the game have lifetime TA's above 1.000. The immortal Ruth is in a class by himself at 1.432. Henry Aaron, who supplanted Ruth as the home run leader, is 20th on the list with a TA of .980. Better than any other stat, the TA shows why the Babe deserves his immortality.

You don't have to be a die-hard fan to appreciate Boswell. His account of the 1978 Yankees-Red Sox playoff game still reads like a thriller. He's been to the big games and he's met the stars; he's also traveled in the bush leagues and the winter leagues, even in the Little Leagues, to listen to the hopefuls and the has-beens. His beat is baseball, and he's covered it from top to bottom. His own love affair with the game--he was in his glory as the 14- year-old kid who could throw a fastball that "did genuinely awful things"--is woven in among the other articles, and he still has a democratic appetite for the game wherever it is played.

How Life Imitates the World Series is a book without a structure, though it is arranged according to the months of the baseball calendar. It doesn't have an index either, a more annoying omission. And there are only glancing references to baseball's problems, the problems that culminated in last year's strike. Boswell's baseball remains curiously unsullied, archaic, and pristine.

Yet he comes as close to the truth of our mysterious national pastime as any writer in the business. He lets the game speak for itself, and speak it does, robustly, in a great variety and harmony of voices.