Smash Online is a free Massively Multiplayer Online Game, which means you don't have to pay to download and play - for as long as you want.
The game is being financed by small ads (billboards like on real Tennis courts) as well as the sale of virtual items such as shoes, shirts or equipment. These items enhance your gameplay, but you do not have to buy them in order to have fun or compete against others. Many items can even be bought with the in-game currency which you gain by winning matches.