All the players were wearing 42 because it was Jackie Robinson day - April 15, 1947 was his first day on the Dodgers. The first black player in the major leagues since 1880. This was a huge step for Baseball and for this country because it set a very visible example. He was a great and exciting-to-watch player; he endured lots of hate for a while and handled it well.
And at 2:49 there was a minute of silence to remember the Marathon bombing of two years ago.