Assaulting an Existing Combat... Who Fights?

It is hard to imagine someone struggling to understand how Multiple Combats work out. But it may be helpful for someone out there...

I have had this issue come up time and time again. Two units will be locked in hand to hand. Neither unit breaks or is wiped out. On the next turn a fresh unit charges into the melee. The question then comes up - who can swing at who?

Here is the actual wording from the 40k Rule Book as well as the bullet point added in with the errata -

• Models that were engaged with just one of the enemy units at the beginning of the combat (before any model attacked) must attack that unit.
• Models that were engaged with more than one enemy unit at the beginning of the combat (before any model attacked) may split their attacks freely between those units. Declare how they are splitting their attacks immediately before rolling to hit.
• Models that at the beginning of the combat (before any model attacked) were engaged with more than one enemy unit, but were in base contact with just one of the enemy units, must attack that unit [Note - the next rule covered in the Errata also refers to Multiple Combats... reading it may make the rest of this post pointless].

Where a lot of confusion arises out of these rules is what it means by 'beginning of the combat.'

Here we have the section from the INAT FAQ that covers this topic -

RB.41C.01 – Q: The rules on page 41 seem to indicate that a unit fighting in an existing close combat that is charged by another enemy unit cannot direct their attacks at this new threat. Is this correct? A: No. The “beginning of the combat” is after all assault moves are completed, therefore a model in base contact with multiple enemy units can always choose to attack an enemy unit that has just charged it [RAW]. [Note - I prefer to avoid using the INAT Rule Book when it comes to working out rule questions]

When you look at all these different pieces together knowing what the 'beginning of the combat' means it all clicks into place. Whether or not a unit charged into a combat really has no bearing on who gets to swing - you just look at all the models once everyone has moved (but before any attacks are made) and figure out who gets to swing.

There will still be instances where units can't swing at certain units, but this should be a pretty rare case and will not happen near as often as people think.

- Big D in Who Gets to Fight? - Assaulting an Existing Combat

Edit - looks like Taak struggled to understand Multiple Combats.