The National Pastime offers baseball history available nowhere else. Each fall this publication from the Society for American Baseball Research (SABR) explores baseball history with fresh and often surprising views of past players, teams, and events. Drawn from the research efforts of more than 6,700 SABR members, The National Pastime establishes an accurate, lively, and entertaining historical record of baseball.   A Note from the Editor, Mark Alvarez:   It's slipping by unnoticed, but 1993 is the 100th anniversary of modern baseball. A century ago this past April, pitchers for the first time in official play toed a slab sixty feet, six inches from the intersection of the foul lines. This was the last of the great changes made in the game during the vigorous, experimental, unrestrained, untraditional nineteenth century. The diamond was set.   A hundred years ago, baseball was already the national pastime, but it was still a relatively young sport. If we superimpose our year on 1893 and look back, baseball's development seems remarkably rapid. The game broke free from its town ball roots about the time Pesky held (or didn't hold) the ball and Slaughter scored from first. The great, professional Cincinnati Red Stockings took the field the year the Mets stunned everyone by winning a pennant and a World Series. The National League was founded in the year of Mark "The Bird" Fidrych. A walk counted as a hit just six years ago.   In 1893, a 50-year-old baseball fan had lived through the whole history of the "New York Game." Even youngsters of 30 had been able to watch the development of the sport into a business calculated to make money for "magnates," who three years before had crushed a player revolt and who now seemed determined to run the over-large "big League" into the ground. They didn't of course. Outside forces, including Ban Johnson and an improved economy, would soon reinvigorate the game. (Our troubled sport could use another such jolt any time now.)   Sometime this season, maybe you can catch a few rays in the bleachers, or lie in a hammock tuning a lazy ear to a Sunday afternoon broadcast, or--best yet--perch on a grassy hill overlooking a high school game, give the game's past century a thought. And pass it on. Modern baseball is 100 years old.