Sorry I couldn’t find the most recent thread about this, all my searches turned up ten years ago or older. Someone on another forum posted this description and it sounds interesting:
the one in outer space where an early/mid teens boy is forced to fight a man at least twice his age, and much bigger and stronger than him, just to keep his preteen sisters from being forced into child prostitution.<
Paging @Andy_L
It’s been decades since I read it so I won’t vouch for this, but that synopsis tickles a vague memory of the opening chapters of Anthony’s first Bio of a Space Tyrant book.
(And now I have to go cleanse my brain.)
Ditto what @Cervaise said.
You rang? Just from the description, it has the air of Piers Anthony (as the others suggest).
This review Refugee (Bio of a Space Tyrant Series #1) by Piers Anthony, Paperback | Barnes & Noble® says:
"Because he defended his older sister against the violent lusts of a wealthy scion, Hope and his peasant family were forced to flee Callisto, one of the moons of Jupiter. Pursued by the bloodthirsty scions across the airless desert, they barely escaped with their lives. "
Thanks all!