A Miami Marlins fan proposed to his girlfriend during the ceremonial first pitch. Marlyn Sanchez, who has sung the national anthem at games before, was proposed to by her boyfriend.
The boyfriend posed as the catcher, and despite her terrible first pitch, he proposed. She said yes and they will live happily ever after.
I'm not a fan of the stadium proposals, unless she says no. Those are fantastic.
With that said, if you're going to do a stadium proposal, a Marlins game is one of the best places to do one. Nobody shows up at their games, so if she says no, you're not humiliated.