MMO games, including MOBAs, compose 21% of the worldwide digital game market and are on track to generate $11 billion in revenue this year alone, SuperData Research reports. By 2017, that number is expected to rise to $13 billion. In 2014, the No. 1 MMO in terms of revenue is League of Legends, which has so far generated $946 million, beating out subscription games such as World of Warcraft, which is No. 4 on the list with $728 million.