In American Football the offensive side must have seven players on the line of scrimmage. At one time it could have more. If they did today, then the players between the ends would need to have interior linemen numbers.
Rules require at minimum 7 players to be on the line for any play. If a goal line offense has a RB and FB then the line might have 8 on the line.
The offense is allowed up to ten players on the line of scrimmage, need one to receive the ball from the center. But the offensive is required to have a minimum of seven players on the line of scrimmage. Defensively all eleven can play on the line of scrimmage.
4 players or a computer that does the 4 players
Seven, of which two are eligible receivers. All other offensive players must be at least one yard behind the line of scrimmage (the exception being the quarterback) for one second before the ball is snapped.
11 players
You need to have 6 players to form a team and you need to have a coach...but you can have as many as you want as long as you have enough uniforms.
two
The team is out when three players are out.
15
one, you
There should be 22 players on the field 11 players from each side are allowed.