That goes back to the early days of football, when mass plays like the flying wedge were making the game so violent that Teddy Roosevelt threatened to ban the game altogether. Requiring that at least seven players always remained on the line of scrimmage opened up the game for ball carriers and kept the chance of dangerous mass plays to a minimum.
In American football, they guard the scrimmage line.
As far as the NFL is concerned, if both wide receivers are on the same side of the field and on the line of scrimmage, the formation is illegal. There must be 7 players on the line of scrimmage and 3 players on each side of the center. It sounds like your question is describing a situation where there are 4 players on the line of scrimmage on one side of the center and 2 players on the line of scrimmage on the other side of the center. If this is the case, the formation would be deemed illegal and result in a five yard penalty being called against the offense. It is illegal to have a receiver 'covered' by another receiver on the line of scrimmage.
There have to be at least 7 men on the line of scrimmage for the offense. There are no requirements for the defense.
Seven on offense. No requirements for the defense
It ussually has no fullbacks. It is a one back style of offense.
Wishbone, waivers, wildcat formation, west coast offense and walk-on are football terms.
Its a split back formation where the running backs line up closer to the line of scrimmage behind either the guards or the tackles and are side by side as opposed to in a line like an I formation. There is typically a tight end and two wide receivers. The formation allows for running and passing as the backs (two RBs or a RB and FB) are close to the line and can serve receive as receiving options in addition to running. It's most commonly associated with Bill Walsh's West Coast offense.
In HS: On offense, there must be seven or more players lined up on the line of scrimmage when the ball is snapped. If there are less than seven offensive players on the line of scrimmage at the time the ball is snapped the penalty is called an illegal formation. (if there are more than 7, some players that would normally be eligible to be downfield for a pass are ineligible, but it is still a legal formation). In NCAA/NFL: There must be 4 players in the backfield (off the line of scrimmage) at the snap. While the two rules sound the same, the difference occurs when the offense doesn't have all 11 players on the field. In high school, it means less players in the backfield. In the upper levels, it means less players on the line of scrimmage (and it makes the job of the short-wing officials a lot easier when checking the formation). There are also some other rare/unusual rules when governing legality of formations, such as HS requires a man on the line of scrimmage on both sides of the center (usually the guard), in college and pros you need two players on both sides of the center on the line of scrimmage (usually the guard and tackle). Also, the 5 players on the line that are ineligible (the offensive lineman) must wear numbers of ineligible receivers (between 50-69). There is an exception to the player numbers on 4th down FG attempts and PATs.
On the offensive side, nobody has to be in a down position on the line of scrimmage, but there must be six men on the line. The defense does not have any regulations as to where they must line up on the line of scrimmage.
Where the offense left the line of scrimmage
The "invisible" line in football is the Line of Scrimmage.The Line of Scrimmage is the line that divided the offense from the defense, which is located at the tip of the football after it has been placed on the ground, also known as spotting the ball, by the referee. The line extends from sideline to sideline. Players cannot cross the line of scrimmage until the next play begins, and if they do a penalty can be called.If the offense crosses the line of Scrimmage before the ball is snapped, the following penalties can be called:Offsides: 5 yard penalty - This penalty is almost exclusively called on the defense because if an offensive player moves across the line of scrimmage, that player is typically charged with a False Start penalty.If the Defense crosses the line of Scrimmage before the ball is snapped, the following penalties can be called:Neutral Zone Infraction: 5 Yard penaltyEncroachment: 5 yard penaltyOffsides: 5 yard penalty
The offense must have 7 players on the line of scrimmage.