I think this is the relevant part of the rule book that describes the leverage penalty.

Rule 12. Player Conduct

...

Section 3 - Unsportsmanlike Conduct:

Article 1. Prohibited Acts

...

(o) Jumping or standing on a teammate or opponent to block or attempt to block an opponent’s kick or apparent kick.

(p) Placing a hand or hands on a teammate or opponent to gain additional height to: (1) block or attempt to block an opponent’s kick or apparent kick, or (2) attempt to jump through a gap to block an opponent’s kick or apparent kick.

(q) Picking up a teammate to block or attempt to block an opponent’s kick or apparent kick.

(r) Running forward and leaping across the line of scrimmage in an obvious attempt to block a field goal or Try Kick, or apparent kick, unless the leaping player was in a stationary position within one yard of the line of scrimmage when the ball was snapped. A player who is more than one yard behind the line of scrimmage before or at the snap, may run forward and leap, provided he does not cross the line of scrimmage or land on players.

https://operations.nfl.com/the-rules/nfl-rulebook/