Hall lays out his beef with Oates in legal docs the judge is now unsealing ... and they reveal exactly why the legendary duo is at war. As we reported, Daryl got a restraining order last week against John, and we now know he got it to block the sale of John's half of Whole Oats Enterprises (WOE) -- a company they'd formed to control some of the group's assets.

In the docs, Daryl explains they'd agree to a business divorce, of sorts, in 2022 ... where they'd start splitting up assets. Where things went south, according to Daryl, is when John secretly decided to sell his half of WOE to a company called Primary Wave.

Daryl says he was "blindsided" by this decision -- which was revealed to him 2 days before he was leaving on a tour ... and he thinks John's timing was intentional. According to the docs, John knows he needs Daryl to approve that sale, and Daryl says, "I have no intention of becoming partners with Primary Wave, and [Oates] cannot be permitted to thrust a new partner upon me in this outrageous fashion."

And here's a sign of how petty this is getting ... Daryl even thinks John timed the Primary Wave deal to coincide with start of Daryl's tour to "ambush" and distract him, potentially screw up his performance ... and intentionally "cause me the maximum amount of harm."

As for why Daryl's saying "I Can't Go For That" with Primary Wave -- in the docs, he says the company has a rep for exploiting copyrights and trademarks of artists after purchasing their catalogs. Bottom line, he doesn't want PW controlling his name and likeness.

He wants the dispute to be settled in arbitration, and until it is ... he wants a judge to block Hall's sale to PW.

If you wanna know just how nasty this split is, consider this -- it's almost a carbon copy of what Brad Pitt and Angelina Jolie are going through in the war over their French winery ... where she tried to sell her half to a Russian oligarch, pissing off Brad.