Given the question: Information: - United Indoor Football (UIF) was a United States indoor football league that started in 2005. Ten owners from the National Indoor Football League, including one expansion (the Dayton Warbirds, which never played a game in UIF) and two from arenafootball2 (af2) took their franchises and formed their own league. The league was based in Omaha, Nebraska. - In the United States, indoor football is football played at ice hockey-sized indoor arenas (as opposed to certain NFL teams which have large indoor stadiums, such as the New Orleans Saints who play in the Mercedes-Benz Superdome). While varied, the rules of indoor football are designed to allow for play in a smaller arena. The indoor football season typically begins in mid- to late-winter and ends by mid-summer. - The Ultimate Indoor Football League ( UIFL ) was a regional professional indoor football league that began its inaugural season on February 18 , 2011 as the Ultimate Indoor Football League before playing as the United Indoor Football League in 2012 , then switched back to '' Ultimate '' for the 2013 season . After the 2014 season , the league merged with X-League Indoor Football . - The Indoor Football League (IFL) is a professional indoor American football league created in 2008 out of the merger between the Intense Football League and United Indoor Football. For the 2015 season, the league had ten teams. The league is the second highest tier in indoor/arena football behind the Arena Football League (AFL). IFL players earn a minimum of US$250 per game played (before taxes). The season is 16 games long, plus playoffs of two or more rounds. - The Arena Football League (AFL) is a professional indoor American football league in the United States. It was founded in 1987 by Jim Foster, making it the third longest-running professional football league in North America, after the Canadian Football League (CFL) and the National Football League (NFL). The AFL plays 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 Foster, a former executive of the United States Football League (USFL) and the NFL. - Arena football is a variety of indoor gridiron football played by the Arena Football League (AFL) and China Arena Football League (CAFL). 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. - The Intense Football League (IFL) was a professional indoor football league that initially began operations in 2004. Its focus was in Texas, but was notable for being the first professional football league to place a franchise in Alaska. Given the paragraphs above, decide what entity has the relation 'sport' with 'indoor american football'.
The answer is:
ultimate indoor football league