What is the penalty for an ineligible man down field?

Answer 1

That could mean a couple of things. On a pass play, offensive lineman (center, guard, tackle) are not allowed to cross the line of scrimmage prior to a pass crossing the line of scrimmage. This infraction is called ineligible man down field. On a punt, the only players on the punting team allowed to cross the line of scrimmage prior to the punt are the two players positioned on the end of the line. Should any other player except for those two players cross the line of scrimmage prior to the punt, the infraction is called ineligible man down field.

Answer 2

The penalty for an Ineligible Receiver Downfield is 5 yards.