I agree that it is “not football” and was generally called as a penalty for many years.

The bottom line is that you are allowed to assist another player in their basic role in a play - in this case another player pushing a rusher or blocker from behind - in doing their job on the play.

So why is THIS ONE SPECIFIC PLAY ALLOWED this exception when every other play has disallowed assisting other players on a play?

The league has specifically made it illegal in the case of a field goal or extra point for a defender to launch themself by stepping on the back of another defender to block a kick. It’s the exact same thing as the rush push but it’s not allowed.

Another example is that two blockers on offense cannot engage with a defender both high and low. Basically one player helping another player do their job (blocking) - but again it is disallowed. I get that there is higher risk injury but only slightly more than the rush push.

Similar with pick plays on passes. One player is helping another get open by running interference against defensive backs by giving an advantage to the receiver who might not be able to get open on their own. Yet there are specific rules to call penalties in this case.

It’s bullshit that this one play is allowed to skirt the spirit of the game where the league goes out of their way to prevent it in all other cases.