The crossword solution for the term 'Bag or Ball Lead-In' is AIR, which is a three letter word. AIR is a naturally occurring substance composed of nitrogen, oxygen, and other gases, and is essential for all known forms of life. It is the most abundant element in the Earth's atmosphere, and is the source of oxygen for living organisms. AIR is also used to power many machines, such as aircraft, and is used in many industrial processes.