NFL has a rule about roughing the passer. You'll know how it works; and that quarterbacks don't dummy passes with oppo players in close proximity. Is your claim that Rugby Union players are more skilful and/or have more control of their bodily movements than NFL defense players?
Even the NFL recognises that a committed defensive player cannot expect to pull out of a tackle at the last monent. That is why they have the "One Step Rule"
Rule 12 Section 2 Personal Fouls
ROUGHING THE PASSER
Article 13 Because the act of passing often puts the quarterback (or any other player attempting a pass) in
a position where he is particularly vulnerable to injury, special rules against roughing the passer apply. The
Referee has principal responsibility for enforcing these rules. Any physical acts against passers during or
just after a pass which, in the Referee’s judgment, are unwarranted by the circumstances of the play will
be called as fouls. The Referee will be guided by the following principles
PASS LEAVING PASSER’S HAND; ONE-STEP RULE
(1) Roughing will be called if, in the Referee’s judgment, a pass rusher clearly should have known that the
ball had already left the passer’s hand before contact was made; pass rushers are responsible for
being aware of the position of the ball in passing situations; the Referee will use the release of the ball
from the passer’s hand as his guideline that the passer is now fully protected; once a pass has been
released by a passer, a rushing defender may make direct contact with the passer only up through
the rusher’s first step after such release (prior to second step hitting the ground); thereafter the rusher
must be making an attempt to avoid contact and must not continue to “drive through” or otherwise
forcibly contact the passer; incidental or inadvertent contact by a player who is easing up or being
blocked into the passer will not be considered significant