The game commences with the tip-off, when the referee tosses the ball into the air over the center circle, in which the opposing centers stand face to face. The centers then leap into the air and attempt, with their hands, to tap the ball to their teammates. The team that gets the ball attempts to advance it toward the basket defended by the opposing side, in order to try for a field goal, or basket, scoring two or three points, depending on the player's distance from the basket. A player may advance the ball by passing it to a teammate or by bouncing (dribbling) it continually along the floor while running toward the basket. If a player walks or runs with the ball without dribbling it—a violation called traveling—that player's team surrenders possession of the ball. After a basket is scored, the opposing team puts the ball into play from behind its end line and in turn tries to move the ball upcourt to score.