Boxing is returning to Boston’s Fenway Park for the first time in nearly 70 years. “Fight Night at Fenway” is scheduled for Saturday. The 11-fight card is the culmination of years of effort by twin brothers and longtime public schoolteachers who grew up in Watertown. Matt and Mark Nolan want to revitalize boxing in the city that was home to some of the greatest athletes in the sport’s history. It’s also symbolic of a shift back to the roots of the oldest ballpark in Major League Baseball. In the past, Fenway has held political events and sports like football, soccer, hockey and basketball, not just Red Sox games.