There's no explanation for how "Take Me Out To the Ball Game" became the song to sing during the 7th inning stretch. Actually, it has been sort of replaced by "God Bless America" since 9/11 and that actually just makes me want to hear "Take Me Out To the Ball Game" more. What's even more interesting is that there's no good reason why baseball's "halftime" is in the middle of the 7th inning and not, say, the middle of the 4th.
Just proves that baseball needs to cut back on the number of innings.