Imagine one unit which is bold in attacked in one turn by three units. Say it survives the first unit attack and because it is bold it gets a battle back. In the same turn, another units attacks it, I would say that it now does not get a battle back against the second unit as it is not the initial attack. Similarly I would argue against the third unit attack it does not get a battle back as it in the same turn. Do you agree?

It took me a couple of days, but I've designed a super computer to answer your question. Fortunately it did not make me wait 7.5 million years to receive the answer. Unfortunately the answer it gave me was "42".

The above post was much more apropos when the original post showed only as a runtime error

Now to answer the question posed in straight fashion: The defending unit in question would be able to battle back as long as it maintained its position upon the original hex. I like it this way. Still plenty of benefit to ganging up, but a well positioned unit will be hard to dislodge.

Let me amend Todd's answer (to a certain extent)...the original hex is the HEX it is on for the first attack. Since Calvary units can have a follow on attack and the 2nd attack against that same unit would NOT get a battle back for the calvary 2nd attack, even if it moved to a bold position.

But that's not the original hex of the battle, is it?

In all seriousness, the available circumstances do open themselves up to all sorts of word parsing, but until a rule change or unit ability comes along to alter it, each unit only gets one battle per turn - though that battle may include multiple attacks due to the unit's abilities and lore plays, etc. A unit gets as many battle backs per turn as opportunities arise that permit them. As Caboose points out, if a unit moves from its original hex due to an attack from a particular unit which then continues its battling by attacking that same defending unit again, regardless of whether that defending unit holds its hex during subsequent attacks from that attacking unit, it will not be eligible to battle back until attacked by a different unit. Not really as complicated as that all sounds...