In the NCAA rules, the only description of the Ineligible Receiver Downfield penalty is below. It can only be called on a forward pass that crosses the line of scrimmage. Since a punt isn't a forward pass, the linemen are able to release as soon as the ball is snapped.
Ineligible Receiver Downfield
No originally ineligible
receiver shall be or have been more than three yards beyond the
neutral zone until a legal forward pass that crosses the neutral zone
has been thrown (A.R. 7-3-10-I and II). PENALTY—Five yards from the
previous spot [S37].
In the NFL rules, there is a specific provision regarding players on the line during scrimmage kicks:
KICKING TEAM PLAYERS ON LINE DURING KICK
Article 2 During a kick from
scrimmage, only the end men (eligible receivers) on the line of
scrimmage at the time of the snap, or an eligible receiver who is
aligned or in motion behind the line and is more than one yard outside
the end man, are permitted to advance more than one yard beyond the
line before the ball is kicked.
Penalty: For advancing more than one
yard beyond the line of scrimmage before the ball is kicked: Loss of
Although I don't see it clearly described in the NCAA rulebook, lineman are allowed to release downfield immediately after the snap on a punt where in the NFL they must wait until the kick. The change in rules is indicated by the offense using a Scrimmage Kick Formation, which is defined in the NCAA rulebook:
Scrimmage Kick Formation
a. A scrimmage kick formation is
a formation with at least one player seven yards or more behind the
neutral zone, no player in position to receive a hand-to-hand snap
from between the snapper’s legs, and it is obvious that a kick may be
attempted (A.R. 9-1-14-I-III).
b. If Team A is in a scrimmage kick
formation at the snap, any action by Team A during the down is deemed
to be from a scrimmage kick formation.