The last couplet refers to the fourth couplet (seven and eight sentences) of the verse. No need to fight. It is named after its placement at the end of a poem.
For example:
Suddenly there was a message from Jibei outside the sword.
When I first heard it, my clothes were filled with tears.
But what’s wrong with my wife?
The poems and books are full of joy.
You must indulge in drinking while singing during the day,
Youth is a good companion for returning home.
That is, cross Wu Gorge from Ba Gorge,
then go down to Xiangyang towards Luoyang.
The last two sentences of this poem are completed in one go, a kind of flowing water pair (see below for details on flowing water pairing). It's still quite different from ordinary battles.
In general couplets, the first couplet and the second couplet are two parallel sentences, each with complete meaning. But there is also a kind of contrasting first and second couplets that often go together in one go. It makes no sense to read them separately, or at least incompletely. This kind of couplet is called running water pair.
Two sentences in the same couplet are two sentences in form, but their meanings are not contradictory to each other. In fact, the whole sentence is divided into two sentences. In other words, when understood, these two sentences should run through them like running water. That’s why it’s called a running pair. For example, "Look at the wisteria moon on the stone, reflecting the reed flowers in front of the island." Note: Running pairs often appear in tail couplets.