From BR Bullpen
"There are Opening Day pitchers and pitchers who start on Opening Day." - manager Roger Craig
Opening Day is the first game of the baseball season, though there is some imprecision in usage. It is most often used on a team-by-team basis to refer to that team's first game of the season, but occasionally used to mean the first day of the season even if not every team has a game that day or to refer to the first home game for a given team (more often called the home opener).
Opening Day, and home openers for teams that begin the season on the road, is treated as a special occasion. It is their first opportunity to show off new players, new uniforms, and stadium improvements. Teams will pull out all the stops when searching for singers for the National Anthem and participants for the first pitch ceremony. Teams may schedule the game at an unusual time, like having a weekday game during the daytime instead of at night, or have extra promotions.
While several pitchers have thrown shutouts and one-hitters on opening day, Bob Feller remains the only MLB pitcher to have thrown an opening day no-hitter, on April 16, 1940. Leon Day pitched an opening day no-hitter as well in the Negro National League on May 5, 1946.