Why does every game seem to start with the national anthem?

Before the opening kickoff, first pitch or tipoff, Americans are often asked to stand for “The Star-Spangled Banner.” But the national anthem did not begin as a sports tradition. Its words came from the War of 1812, when Francis Scott Key watched the British attack Fort McHenry in Baltimore. Seeing the American flag still flying inspired the poem that became the song, according to the Smithsonian Institution.