The first baseman was wearing number 42. So was the catcher and pitcher. All the Oakland Athletics were, and so were their opponents, the Astros. 42 was the only number across the landscape of the Major Leagues, April 15, because 70 years before, on that day, Jackie Robinson wore 42 and became the first African-American to play ball in the majors. It might have been the most important moment in baseball history.