Sports are seen as a catalyst for international communication. Even the Olympic Games were established a century ago to promote world peace — through people meeting and competing on level playing fields.
Never mind linguistic, historical, or cultural differences. The rules of the game are understood, bodies get trained to peak health, and the young learn the value of team spirit and sportsmanship. In other words, give people a ball and a goal, and let friendships form. Unless you are a foreigner in Japan.