Sorry ... neglected to answer this part. If R left the field and blocked, then he's guilty of IP as well. 9-6, not 9-4.

This is what I was thinking of. But given this play, I'm not sure I agree with the rest of this sentence. By running 15 yards OOB and taking a blocker with him, he's definitely participating, even if the play ends shortly after he re-enters.

I just can't see flagging R here but giving K a pass, since K's illegal actions occasioned R's.

Yep, I see that now. I was looking at the provision of the IP rule that prohibits A/K from leaving the field (9-6-1 rather than 9-6-2), and addressing the idea that R hitting K OOB might be a PF (hence the reference to 9-4).

Not true. R's foul occurred significantly before anything K did illegally. K was blocked OOB, K tried to return, then R went out of bounds and participated by blocking. That should be flagged the moment he left the field of play and then blocked. You don't know (yet) that K is going to foul.

You may, or may not, still have a foul on K later in this play, either by participating in the actual play or as you described, occupying a blocker. However, I think you'd get some debate on the idea that K running out of bounds 15 yards occupied a blocker. The players are supposed to know the rules - if K doesn't return immediately, R should know to ignore him. I can see your side too though, especially with the K player running right in the restricted area - near enough to inbounds that R feels like he needs to stay with his man.

I hear this a lot when talking about IP, but its when he steps back on field the foul has occured, not only if he " does something"

Not if he stepped out intentionally (which would be rare). Then he's guilty of IP merely for participating.

Not sure what you are saying. If he intentionally steps out, you have a hat down, not a flag. If he doesnt re-enter field during the down, there is no foul

No, mere reentry is not IP. PARTICIPATING (at all) is required for illegal participation.

Imagine the play nearing it's end on the other sideline, our OOB WR walks back onto the field, or even jogs back on while heading to his own sideline --- if he is not involved in the play and no one from the other team reacts to him, he has not participated.

I would like to see NFHS clarify 9-6-1 and 9-6-2. The letter of the rule, especially 9-6-2, states that it's a foul to return to the field. "No player shall intentionally go out of bounds during the down and: (a) Return to the field."

However, the concept and philosophy of illegal participation is that merely stepping on the field, with nobody else around, is not participation and does not warrant a flag. Provided that one understands 'participation' broadly enough — not just catching a pass, but also occupying a blocker, for instance — it's reasonable to require the player who went OOB to participate before penalizing his team 15 yards for illegal PARTICIPATION.

Between that and the slippage about what constitutes "intentionally" going OOB, this rule needs some editorial revision. I'd be happy to consult, if you're reading this post, NFHS rules committee members. :)

OK, so if receiver A1 intentionally goes out of bounds, A2 catches ball, as A1 re-enters field, then blocks, where is the flag down? Where he re-enters or where he blocks? I agree with poster above, the foul occurs when he steps back onto the field, now what he does after that, unless that, is also illegal. I also get "philosophy" says we turn our head unless he "does something"...but what if that is 30 yards down the field?

Oh, that's easy. The spot of the foul is defined by rule as where he re-enters. 9-6-2

Exactly, then we have answered our question, the foul is where he re-enters the field during the down.