Water polo is a water-based team sport played by two teams of seven players each. The game is divided into four quarters during which the two teams try to score goals by tossing the ball into the opposite team's goal. The contest is won by the side with the most goals at the end of the game. Water polo is often referred to as "swimming pool football" because of its similarity to American football. However, water polo has several important differences from American football: there are no downs, points are scored instead of lost when the ball goes out of bounds, and there is no stopwatch used to determine time left in the game. The first Olympic medal awarded for water polo was given to Sweden at the 1920 Antwerp Games. Since then, only gold medals have been awarded. No country has ever won more than three water polo medals at one Olympics. At the 1952 Helsinki Games, the Soviet Union became the first country to win five gold medals in a single edition of the Olympics when it dominated the event. It has since become a tradition for them to finish among the top two every time they participate in water polo events. The United States has the most overall victories with 116. Italy is second with 57 wins. Both countries have many prominent water polo players. They have also participated in most Olympic games. China is the third most successful country with 53 wins.