In football, the offense needs to put at least seven players on the line of scrimmage on each play. The offense is able to put more players on the line of scrimmage if they prefer.
Putting less than seven players on the line of scrimmage is going to result in an illegal formation penalty.
The defense can put as many players as they want on the line of scrimmage. On PATs, field goals and punts the defense is not allowed to place more than six defenders on one side of the snapper.
Source – Rule 9 Item 2 (2) – NFL rulebook
Offensive players on the line of scrimmage
On the offensive side of the ball the line of scrimmage is going to play a large role. Players that are lined up on the line of scrimmage are going to have different rules apply to them.
For example, only the two players on the end of line of scrimmage are eligible receivers.
All players that are on the line of scrimmage but not on the end are not allowed to catch passes.
This is why you may have heard an announcer state that a player was “covered up”. This means a player was on the line of scrimmage yet not on the end.
Since they were “covered up” by the furthest outside player on the line they are therefore not eligible to catch passes.
Generally speaking most offensive players on the line of scrimmage are going to be offensive linemen. For each play, you can expect the offense to have five offensive linemen on the line of scrimmage.
Most teams will then use two wide receivers or a wide receiver and a tight end as their other two players on the line of scrimmage.
On some occasions, an offense may use more offensive lineman. This is mostly done in short-yardage situations when heavier players are needed to push the pile.
In these situations, the offensive lineman are going to make up the majority of players on the line of scrimmage. This can often result in offensive linemen being eligible receivers.
When this happens the lineman must announce to the official that they are an eligible receiver. This is only the case when an offensive lineman is the last player on the line of scrimmage on their side of the field.
Defensive players on the line of scrimmage
When it comes to defense football tends to be much less harsh for illegal formations. So long as the players do not cross into the neutral zone or past the line of scrimmage then penalties will rarely be called.
When playing defense in football a team may put as many players they want on the line of scrimmage.
Offense formations are limited because they cannot allow every player to be an eligible receiver. If all players were eligible it would be nearly impossible for the defense to cover everyone effectively.
Defense on the other hand does not gain any specific advantage when putting more players on the line of scrimmage. There is no rule for defensive players on the line of scrimmage because there simply doesn’t need to be one.
The only time the line of scrimmage comes into play for defensive players is during special teams.
The reasoning for this rule is quite obvious. If all eleven defenders all lined up on the right side of the field punts would look a lot different.
Without adjustments by the offense the defense would easily overrun the blockers and block the kick/punt.
For this reason, the defense must spread their players relatively evenly across the line of scrimmage on these special teams’ plays.