What does deo mean when sung at a baseball game?

Answer 1

It's "Day-O ("The Banana Boat Song)," which was a big calypso hit for Harry Belafonte. The song has a rhythmic call-and-response flavor, so Baseball teams frequently play the opening call during rallies, knowing that fans in the stands will repeat it.

Answer 2

"Deo" is a shortened version of the Latin phrase "De Profundis," which means "out of the depths." It is commonly sung at baseball games to pump up the crowd and show support for the team. So, in a nutshell, it's just a fancy way of saying "Go team, go!"