Tekken Ball is one of the mini-games that can be played in Tekken 3, it's played by attacking the volleyball as it come to your side of the field, different attacks carry the ball differently. Some attacks against the ball won't hurt your opponent at all, while others can deal a good amount of damage. If it's your turn and the ball falls on your turf, then it's considered a foul, sometimes causing you damage and vice versa for the CPU.
There's three balls to choose from: Beach Ball, Gum Ball and Iron Ball. The damage dealt differs depending on which ball you select.
Playing Tekken Ball also lets you unlock Gon, if you haven't unlocked him already. He's also the first opponent you face in Tekken Ball once you unlock it. Tekken Ball also takes place at Gon's stage.