Normally Baseball players say, "Batter Up."  But this professional Baseball player doesn't really need to say that..He practices his swing by using (drum roll) yes a piece of Bubble Gum!  So I guess he'll be saying "Bubble Up"

Not only did he take several dry hacks in the on-deck circle — like anybody would coming off the bench — but he got in one live round by spitting out a considerable wad of gum and swinging at it.