I had the privilege of attending the 2011 Panamerican Games last month, and went to the brand new baseball stadium in Lagos de Moreno. The stadium said in big letters:
Estadio de Beisbol

My understanding is that the correct spelling is béisbol.
I know it's common for accent marks to be left out in casual writing, or in all-caps, but this is neither casual, nor all-caps.
Is beisbol a legitimate alternate spelling (and pronunciation) of the word?