We have two definitions of ‘non-incidental contact’. The first, is simply the negation of the definition of ‘incidental contact’ which I quoted in the original post. The second is the one you gave before:
Non incidental contact is any contact that is either dangerous in nature or affects the outcome of a play, regardless of whether the contact occurred after possession was established.
A breach affects the play if the outcome of the specific play may have been meaningfully different had the breach not occurred
Up to this point it is still unclear to me how non-dangerous contact which occurred after the outcome of the play could be considered non incidental. The outcome of the specific play could not have been different had the contact not occurred, because it occurred after the outcome was determined. Then comes the example:
eg if the player would not have been able to intercept the pass without causing significant contact with their opponent.
This is the only place in the rules with the term ‘significant contact’, so I’m not sure how to interpret it, but I’m guessing it definitely doesn’t mean ‘any contact’.
So rephrasing what you wrote:
if a player makes an attempt to block/takes a catch, and significant/dangerous contact occurs after that attempt, and they would not have been able to make the block/take the catch WITHOUT initiating that (significant/dangerous) contact – then that is a foul.
That’s a pretty big difference I think. And it still leaves the question of ‘significant contact’.