Before you load your spinner items, simply add a first item to your spinner that says:
B4X:
spinner1.add("SELECT COMPETION")
Sub spinner1_ItemClick (Position As Int, Value As Object)
If position=0 then
msgbox("Must select an item from the list","")
return
end if
end sub
It would be nice though as @bishmedia said with the prompts because in my app users make a selection from the spinner, and I want to be able to save this selection, and then display it in the prompt of the spinner when the user goes back to the page that the spinner is on so they can remember what they selected.