I don't wrestle or fight, and don't understand Definition 1. Who's wrenching what/who? What's being twisted "round so as to face the opposite direction"?
Retorquere means literally "to wrench or twist back" so in wrestling terms it would mean something along the lines of pulling ones limbs back like getting someone in a leg or arm bar.
The "link" to retort comes in the 2nd, 3rd, and 4th senses, meaning a turning back. A retort is a "comeback" it's turning the argument back on itself. Though it likely originally meant something along the lines of "using one's argument against them" it has come to mean a response or rebuttal in general over time.
I've found many Latin words come into English in a more figurative sense than literal. It's kind of like having to read between the lines.