 The AFL played a proprietary code known as arena football, a form of indoor American football played on a 66-by-28 yard field (about a quarter of the surface area of an NFL field), with rules encouraging offensive performance, resulting in a faster-paced and higher-scoring game.The sport was invented in the early 1980s and patented by Jim Foster, a former executive of the United States Football League (USFL) and the NFL.From 2000 to 2009, the AFL had its own developmental league, the af2.