Each play in football must have at least seven players on the line of scrimmage. The offense can put more players on the line if they desire.
You will be penalized for an illegal formation if you put fewer than seven players on the line of scrimmage.
It is permissible for the defense to place as many players as they wish on the line of scrimmage. However, they cannot place more than six defenders on one side of the snapper on PATs, field goals, and punts.
NFL Rulebook, Rule 9 Item 2 (2)
Offensive Players on the Line of Scrimmage
There are different rules that apply to players lining up on the line of scrimmage on the offensive side of the ball.
It is only the two players at the end of the line of scrimmage who are eligible to receive passes.
It is not allowed for any player on the line of scrimmage but not on the end to catch passes.
An announcer may have stated a player was covered up, meaning they were on the line of scrimmage but not at the end.
Due to their “coverage” by the furthest outside player on the line, they are not eligible to catch passes.
In general, most attacking players on the line of scrimmage will be offensive linemen. On an average play, the offense will have five offensive linemen.
As their other two players on the line of scrimmage, most teams will use two wide receivers or a wide receiver and a tight end.
In short-yardage situations when heavier players are needed to push a pile of players, an offense may use more offensive linemen.
This situation usually results in more offensive linemen on the line of scrimmage, so offensive linemen can be eligible receivers.
If an offensive lineman is the last player on his side of the line of scrimmage, the official must announce that he is eligible to receive.
Defensive players on the Line of Scrimmage
Football tends to be less harsh on illegal formations on defense. So long as the players do not cross into the neutral zone or cross past the line of scrimmage, penalties are rarely called.
Defense in Football Allows Teams to Line up as many Players as they Like.
It would be nearly impossible for the defense to cover all players effectively if all players were eligible to receive.
The defense on the other hand, does not gain any specific advantage by putting more players on the line of scrimmage. There is no rule for defensive players to be on the line of scrimmage.
Special teams are the only time defensive players have to deal with the line of scrimmage.
Field goals, point after attempts, and punts can only be attempted by six players per side.
As a result, punts would look quite different if all eleven defenders were positioned on the right side.
Defenses would easily overrun the blockers without adjustments by the offense.
To achieve this, special teams defenses spread their players fairly evenly across the line of scrimmage.