Try this:
local centerPosition = Position(100, 100, 7)
local players = Game.getSpectators(centerPosition, false, true, 5, 5, 5, 5)
if #players > 0 then
doPlayerSendTextMessage(cid,19,"Existe um jogador dentro da arena aguarde.")
return false
end
--C = centerPosition ; x = area to look...