In our daily cacophony, the national 'pastime' is one of those notes we periodically strike in hopes of hearing a hint of middle C."" ""Baseball's secret is that, for those who appreciate and value it, it has no secrets."" Abrim with aphorisms and insights, Washington Post sportswriter Boswell's first collection of pieces is also snugly anchored in sand-lot-sentimentality: an unbeatable combination for a baseball scribe. ""The Greatest Game Ever Played"" is the '78 Yankee-Red Sox play-off--given a taste for ""utter profound silence"" over the '51 classic's ""raw pandemonium."" ""The Best Manager There Is""? The Baltimore Orioles' prickly, laconic Earl Weaver (""We have had a little rapport. Not too much"")--also featured in ""Why Baltimore Wins More Games Than Anybody Else."" And that brings Boswell to the Big Bang Theory of Killer Innings, and those other unconcealed ""secrets"" of the game. (Keep score thinkingly. ""For one thing, batting average is less meaningful than on-base percentage. . . .) The climax in the analytical line is ""Welcome to the World of Total Average Where a Walk Is as Good as a Hit"" (and where, confirmingly, Babe Ruth, Ted Williams, and Lou Gehrig have the top Total Averages of all time). Another focus is personal. ""where Did You Go? Out. What Did You Do? Baseball"" carries Boswell from ""the streets and alleys of Capitol Hill"" to the Amherst campus where one of the few ""other twenty-year-olds who wanted to play stickball"" is--too-neatly, but who could resist it?--a dud pitcher named Eisenhower (""I always said you couldn't learn real stick ball on the South Lawn""). There are visits to outlying precincts--in the loose month-by-month arrangement, to Puerto Rico for winter ball (the unretouched ""A Country for Old Pitchers""); to the Appalachian League in April (a socio-study, ""Rookies in God's Country""); to the Maryland Industrial League in May (""they say a grown man is too old to play baseball, ""says a 37-year-old, but they never tell you when it's supposed to take place""). That motif--aging--recurs too; see Sandy Koufax and Ted Williams gladly back in uniform. And, yes, there are personality-profiles of today's everyday names: Ron Carew, Steve Carlton, Pete Rose, Reggie Jackson. But readers with a taste for edged commentary over total appreciation may find Boswell's report on Cuban baseball--""one part century-old tradition, one part artistic Latin temperament, and one part first generation communism""--the best thing in the book. One way or another, a Big Bang.