Wikipedia
Opening Day is the day on which professional baseball leagues begin their regular season. For Major League Baseball and most of the minor leagues, this day typically falls during the first week of April. For baseball fans, Opening Day serves as a symbol of rebirth; writer Thomas Boswell once penned a book titled, Why Time Begins on Opening Day. Many feel that the occasion represents a newness or a chance to forget last season, in that all 30 of the major league clubs and their millions of fans begin with 0–0 records.
Opening Day festivities extend throughout the sport of baseball, from hundreds of Minor League Baseball franchises to college, high school, and youth leagues in North America and beyond. Since Major League Baseball generally starts their season first among professional leagues, their Opening Day is the one most commonly recognized by the general public. Most of the minor leagues start a few days later, but within the same week; the short season Class A and Rookie leagues are exceptions, since they begin play in June. (College, high school and youth baseball seasons vary widely depending on location and weather conditions.) Opening Day ignores the exhibition games played during spring training in the month leading up to Opening Day.
"Opening Day" is the third and final segment of the tenth episode from the first season (1985–86) of the television series The Twilight Zone.
Usage examples of "opening day".
He had a flashing glimpse of gigantic machines in the room, machines that dimly resembled the ultramodern astronomical observatory on the moon that he had visited on opening day two days before.
Obviously I cannot comment on the conduct of all, or even the majority of, military commanders under these circumstances, but the behavior of my employer on the opening day of the Fat Chance Casino showed little of this passive enjoyment.