The NCAA Men's Division I Basketball Championship is a single-elimination tournament played each spring in the United States, currently featuring 68 college basketball teams, to determine the national championship of the major college basketball teams. The tournament, organized by the National Collegiate Athletic Association, was created during 1939 by the National Association of Basketball Coaches, and was the idea of Ohio State University coach Harold Olsen. Played mostly during March, it is known informally as March Madness or the Big Dance, and has become one of the most famous annual sporting events in the United States. The NCAA has credited Bob Walsh of the Seattle Organizing Committee for starting the March Madness celebration during 1984. The tournament teams include champions from 32 Division I conferences, and 36 teams which are awarded at-large berths. These "at-large" teams are chosen by an NCAA selection committee in a nationally televised event on the Sunday preceding the First Four play-in games, currently held in Dayton, Ohio, and dubbed Selection Sunday, as detailed below.