After a while, the attacking or at least counterattacking possibilities of playing close behind the scrimmage (which later came to be called "scrummage") came to be recognized, and some players stationed themselves between the forwards and tend as "half-tends".
The terms became hyphenated and eventually unhyphenated single words, "quarterback" (QB), "halfback" (HB), and "fullback" (FB).
The lack of quarterback in the English-Scottish nomenclature for rugby led to the position name "scrum-half" to distinguish the halfback playing close to scrimmage (renamed "scrummage" or "scrum") from another who would "stand off" from it or "fly" away—the "stand-off" or "fly-half".
It became customary for six to eight of the other players to continue as what might be known in rugby as loose (non-packing, i.e. not binding together) forwards who in Canadian football formed "winglines" on either side of the scrimmage.
The centre scrimmager of the side entitled (and required) to do so would put the ball down in front of him for play-by scrimmage, while both sets of three bodies each ("formed into one compact body" as the rules specified) were crouched and shoving forward at each other, probably meeting at the shoulders as do the front row of forwards in rugby's set scrummage.
The position names in the winglines were retained for a while but eventually replaced by the American nomenclature, although it was not until the 1960s, that Canadian rules required seven players on the offensive line, unless they were playing short handed.
"Centre" even became the rule book designation of the snapper, although as in the American version, there is no necessity that the player who snaps the ball have equal numbers of teammates flanking him or her on the line.
Over time, the typically fast back who played fullback, on offense and defense, was replaced by a heavier one who presented a greater threat to run with the ball more or less straight ahead, and to tackle his opponent trying to do the same.
[5] Confusion increased when the legalization of the forward pass made it more advisable for teams to defend with fewer on the line of scrimmage and more behind.
A common defensive formation was the 6-2-3 or 6-2-2-1, shown below arrayed against an offense's straight T: The so-called center and fullback are playing left and right versions of the same position.
However, that did not become the usual way to name that position until platoon football became common, with players specializing in offense or defense, substituted according to which team has the ball.
There seems to have been some tendency for defensive positions to be named for where the player would play on offense, although quarterback and safety formed an early exception.
However, the bottom illustration needs further explanation, having eliminated the halfbacks and introduced a new position name, "tailback" (TB).
In this version the player may stand as deep as any other back, but there has been a reluctance to identify formations in American football as having more than one fullback (or tailback—see below), although two-fullback systems were not uncommon at one time in rugby.
Another justification is that the player positioned as the left halfback in the top illustration tends to have the fullback characteristics described above.
Even when two players positioned to take a thrown snap in a single wing formation are level with each other (i.e. at equal depth), the faster one (usually playing weak side) is often called the tailback and the more massive one the fullback.
ASCII art (letter diagrams) cannot show this fine a detail, but a quarterback in position to take a handed snap is allowed by rule to stand farther forward, in a place which would otherwise cause illegal confusion as to whether the player was in the backfield or the line.
Instead of wingbacks or conventionally placed halfbacks, an offensive team could have backs positioned wide of the rest of the formation, similarly to a split end, to be pass receivers.
A recent diagram of a short punt formation for offense in youth football had no quarterback, but two fullbacks at the depth of the QB shown above, and a halfback at the position labeled FB above.
[citation needed] And many is the time when a player in the farthest back position, in a formation similar to the short punt shown above, is referred to as quarterback!
[citation needed] Offenses and defenses continued to adapt to the increases in forward passing favored by the rules.
A formation with more than two safeties could have them described by their relative geometric placement—outside, shallow, deep, etc.-but such is not general practice; however, see the discussion of the "nickel" below.
From the description above of the straight T, this formation can be seen to be derived by splitting one end and moving the halfback on the opposite side to a flanker position.
In the 1960s, teams would distinguish between split ends (e.g. the New York Jets professional football club's George Sauer) and flankers (e.g. his teammate, Don Maynard) on their player rosters.
For a relatively brief period, game rules had been adopted in some codes, requiring different uniform numbers for line players from those of backs, and the position naming distinction carried on for a while after the rules were amended to require only certain sets of numbers for ineligible and eligible receivers of forward passes.
At the time they snap the ball, the team is required to have seven players (minus any number their side is playing short in Canadian football) on their line of scrimmage, which includes split or tight ends, but not flankers or wingbacks.
The diagram below of an "ace" formation deliberately mixes terms/symbols for wide receivers: On the left are represented the more traditional and descriptive terms "end" and "slotback" (SB).
Coaches, having no motivation to publicize their plans, usually adopt cryptic codes for certain positions, using letters, numbers, or short names for their convenience.
It is likely that "H-back" is a term derived by back formation (pun unavoidable) from the abbreviation for halfback, although arbitrary letter designation by some coach is just as good an explanation.
This is similar to the short punt formation shown previously, except that potential forward pass receivers are more widely spread.