Arena football is a variety of indoor gridiron football played by the Arena Football League (AFL). It used to be a proprietary game (the rights to which were owned by Gridiron Enterprises) but the patent expired in 2007. The game is played indoors on a smaller field than American or Canadian outdoor football, resulting in a faster and higher-scoring game. The sport was invented in 1981, and patented in 1987, by James F. Foster, Jr., a former executive of the National Football League and the United States Football League. Though not the only variant of indoor American football, it is the most widely known, and the one on which most other forms of modern indoor football are at least partially based.