In a game last week we had the following situation. I multi-charged 2 Dire avenger units with an Ork mob and won combat causing both units to flee. One of the units was reduced to 2 models and had to fall back through a wave serpent wreck causing 1 of the DA to trip and die from a failed Dangerous Terrain check. Would the unit now had to take another morale check for taking 25+% causualties in a phase (and auto-fail it and fall back again)?
The relevant passage from the rulebook pg. 44:
The wound obviously wasn't caused by a CC attack, but should we use the starting size of the unit (pre-combat at the start of the assault phase) or the unit size post combat?A unit losing 25% or more of its models during a
single phase must pass a Morale check at the end
of that phase, or else it will fall back. Do not count
casualties caused by close combat attacks, as they
are covered later in C) Losing an Assault.