Until the mid-1960s, the goalposts were similar in design to rugby posts, with the cross-bar and uprights supported by stanchions installed directly underneath the uprights (in the shape of the letter 'H'). A transitional design from this time retained the twin set of stanchions but placed them behind the cross-bar. In this design, the cross-bar and uprights were supported by a set of horizontal, vertical and diagonal stanchions behind each upright. This design was last used professionally in the first Super Bowl. The modern goal posts supported by a single "goose-necked" stanchion (in the shape of the letter 'Y') made their debut in the 1966 CFL playoffs and were adopted by all three professional leagues then in operation (the CFL, NFL and American Football League) the following year, with many (but not all) college football teams also following suit in the years since. The NFL, which merged with the AFL in 1970, had its goal posts on the goal line until 1974. Similarly, in arena football, the field goal is similar to that in American and Canadian football. A field goal in arena football scores three points, unless it is drop kicked, in which case it scores four points. The goal structure in arena football is much smaller than the outdoor game; it consists of a crossbar above the playing surface and wide; this size is also used for most other indoor leagues as well. Uniquely in arena football, the goal posts are attached to nets on either side of the crossbar which are taut to allow the ball to rebound back onto the field of play. The nets are wide and high. These nets do not represent a scoring area, but keep the ball in play and prevent it from entering the crowd.