I try to make it clearer.
1) Bad throw by the QB. Misunderstanding between him and his WR.
2) The defender is about to intercept the ball. NOBODY HAS TOUCHED THE BALL.
3) The WR wants to prevent the interception, so he hits the defender. It is an illegal contact.
So, a yellow flag must be thrown. This is my question: if the WR hadn't made that illegal contact, the defender would have intercepted the ball and advanced it (and maybe even scored). So, I think it would be fair to give the ball to the defensive team.
What does the rule book say? Thanks for your patience. I hope it is clear what I want to say.
It certainly appears you are familiar with international "football" (soccer, futbol, whatever you want to call it). I will call it soccer, for clear distinction. That is a fine sport, but the principals are dramatically different. In soccer, no player (other than the goalie) may physically possess (hold) the ball. There are no distance penalties. Penalties for fouls include awarding possession to the opposing team, because most fouls are about just that - one player illegally hindering an opponents ability to keep team possession, which is constantly changing, by the very nature of the game.
In American football, the ball is to remain in team possession until the offense is unable to advance the ball sufficiently. Fouls are penalized by distance, not by changing team possession. Now, there are instances when a penalty might return possession to an offended team, but there are no fouls for which the penalty itself is awarding possession to the opponent.
Different? Yes. Better? You be the judge. But, that's the way it is.
And, by the way, we only have one color of flag, so no need to say "yellow flag." Just "flag" will suffice. Those are actually "foul markers." We do, also, have "spot markers," affectionately called "bean bags," which are black in NCAA, blue in the NFL. They are typically used to mark potential spots related to distance penalty enforcement, or spots of illegal touching of a loose ball.
Robert