<P> As the passing game evolved, a second wide receiver position was added . While it is possible to move the opposite end out wide for a second split end position most teams preferred to leave that end in close to provide extra blocking protection on the quarterback's blind side . That player was essentially playing the modern day tight end position . Instead of moving the blind side end out, one of the three running backs was split wide instead, creating the flanker position . The flanker lined up off the line of scrimmage like a running back or quarterback, but split outside like a split end . Lining up behind the line of scrimmage gave flankers some advantages . Flankers have more "space" between themselves and a pressing defensive back, so cornerbacks cannot as easily "jam" them at the line of scrimmage . This is in addition to being eligible for motion plays, allowing for the flanker to move laterally before and during the snap . Elroy "Crazy Legs" Hirsch is one of the earliest players to successfully exploit the potentials of the flanker position as a member of the Los Angeles Rams during the 1950s . </P> <P> While some teams did experiment with more than two wide receivers as a gimmick or trick play, most teams used the pro set as the standard set of offensive personnel (a flanker, a split end, a half back, a full back, and a tight end). An early innovator, coach Sid Gillman used 3 + wide receiver sets as early as the 1960s . In sets that have three, four, or five wide receivers, extra receivers are typically called slot receivers, as they play in the "slot" (open space) between the furthest receiver and the offensive line . In most situations, the slot receiver lines up off the line of scrimmage like the flanker position . The first use of a slot receiver is often credited to Al Davis, a Gillman assistant who took the concept with him as a coach of the 1960s Oakland Raiders . Other members of the Gillman coaching tree, including Don Coryell and John Madden, brought these progressive offensive ideas along with them into the 1970s and early 1980s, but it wasn't until the 1990s that teams began to reliably use three or more wide receivers, notably the "run and shoot" offense popularized by the Houston Cougars of the NCAA and the Houston Oilers of the NFL, and the "K Gun" offense used by the Buffalo Bills . Charlie Joiner, a member of the "Air Coryell" San Diego Chargers teams of the late 1970s - early 1980s was the first "slot receiver" to be his teams primary receiving weapon . </P> <P> While the general fan base and most commentators use the generic term wide receiver for all such players, specific names exist for most receiver positions: </P> <Ul> <Li> Split end (X or SE): A receiver on the line of scrimmage, necessary to meet the rule requiring seven such players at snap . Where applicable, this receiver is on the opposite side of the tight end . The split end is farthest from center on his side of the field . </Li> <Li> Flanker / Flanker back (Z or FL or 6 back): A receiver lining up behind the line of scrimmage . Frequently the team's featured receiver, the flanker uses the initial buffer between himself and a defender to avoid immediate "jamming" (legal defensive contact within five yards of the line of scrimmage). The flanker is generally on the same side of the formation as a tight end . As with the split end, this receiver is the farthest player from the center on his side of the field . The flanker is usually lined up just like a split end except that he is just behind the line of scrimmage, therefore being in the backfield and not on the line . </Li> <Li> Slot receiver (Y or SR): A less - formal name given to receivers in addition to split ends and flankers (for example, tight ends who line up wide). These receivers line up between the split end / flanker and the linemen . If aligned with a flanker, the slot receiver is usually on the line of scrimmage, and if with a split end, off the line of scrimmage . As with the flanker position, a featured receiver often takes a slot position with a split end to avoid jamming . </Li> <Li> Slot back: A receiver lining up in the offensive back field . Canadian and arena football allow them to take a running start at the line . They are usually larger players as they need to make catches over the middle . In American football slot backs are typically used in flexbone or other triple option offenses while Canadian football uses them in almost all formations . </Li> </Ul>

What is a slot receiver in the nfl