As to the backfield, the top illustration preserves the principle of the names, reflecting distance from the line. However, the bottom illustration needs further explanation, having eliminated the halfbacks and introduced a new position name, "tailback" (TB). Wingback has been described above, but the "WB" in the above illustration is deeper back than that position name would seem to warrant. That is because this is a "wingback deep" version of the single wing, and the position is named wingback because the player is named for his true wingback position as it exists in other versions. 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.