So in simple terms, does that mean option 1) or 2)? To refresh the memory:-

1) Units are deemed to be 'actively involved' for the duration of the assault if they started the assault within 15 cms of a 'viable' target.
2) Units 'actively involved' are reassessed at the start of each round.

Depends wether you mean,
Remain involved as in stay part of the assaulting/assaulted formation or,
Remain "directly involved" as in can still be targeted and take hits/casualties etc.

In your initial post the Orks that were dragged into the assault,Skorchas and Blitz brigade,would remain part of the assaulting Stompa formation (remaining involved until the assault is concluded). They would not be eligible to take hits/casualties or use their FF attack if they are not "directly involved" in the combat round, although they could take hackdown hits.

So option 2.
But they remain part of the assault until it is fully concluded, so could countercharge if further rounds end in a tie, suffer from hackdowns,becoming broken from losing the assault etc.

Good answers both, but not quite where I was aiming at.
I agree that
- The three formations are considered a single formation until the assault is resolved
- units outside 15cms cannot cause casualties, or be hit by the assault

The Blitz Brigade units were 'directly involved' in the 1st round - and thus were a 'viable target' for support fire.
However in the second round, are the units from the Blitz brigade still considered to be 'directly involved' as a hang over from the 1st round or not (as the deaths of the lead jetbikes had put them outside 15cms of the enemy)?

If they are still considered 'directly involved' (option #1) even though they can no longer contribute to the assault, then they are still a 'viable' target for the support fire of the other jetbike formation. This option draws the same kind of inferences as 'Support fire' does; that such formations are still eligible for the penalties of a nearby assault even though they cannot directly contribute.

Obviously if no longer considered 'directly involved' (option #2), then they are not a 'viable' target and so the support fire fizzles.

If the units in the Blitz Brigade can no longer be assigned hits from "directly involved" enemy units, that is not considering support fire, then they are no longer directly involved, so, they can't be targets of support fire.

They *are* still part of the assault, and would count numbers, BM, etc during assault resolution.

My question is: why weren't those Blitzers counter-charging 10cm to *get* directly involved... doesn't seem very Orky to me...

A countercharge can take someone out of line of sight or out of range of a support formation. Support fire determination after a tie would obviously be re-evaluated after countercharge moves in those cases. Valid targeting is re-evaluated for the directly engaged units as well. I don't think there is any justification for holding over "directly involved" status in this case when it doesn't apply to others.

#2.

Thanks Chroma and Neal

In this case, counter-charging the Blitz Brigade units (towards the nearest enemy) would have moved them closer to the supporting jetbikes and broken coherency, so they elected to stay put.

And we played #2 as well (after some discussion).

Ok, so it is not actually written down anywhere, but it seems that the majority of people favour re-assessing the units 'directly involved' at the start of each round of the assault. Is this something that might get into the FAQ, even though it is a bit of a rarity?