The big thing in that sentence is "Models that were engaged with just one of the enemy units at the beginning of combat (before any model attacked) must attack that unit"
In your case, you are in engaged with two enemy units so the rule doesn't apply and you pick who you want to attack.
I think the rule kicks in when you have 2 units vs two units. Take the example of A and B being units from one army and C and D being units from another army.
If they hit combat where it looks like ACBD so A is not in contact with D it would only be allowed to allocated attacks to unit C.
Just to add, this rule also kicks in for the within two inches rules. So if a model in the unit is not in b2b contact but within two inches of a model that is in b2b he would have to attack that unit. If he is within two inches of two different models each in b2b with a different opposing unit he would then get to direct his attacks where he wants.
I used to roll the dice, Feel the fear in my enemy's eyes
I'm afraid there's no authoritative source for thinking you're an asshole
Last edited by asianavatar; 06-19-09 at 03:44 PM.