Randy Turpin won the British Middleweight Title from Albert Finch who had taken it from Randy's older brother, Dick.
Michael Spinks not so much avenged Leon v Holmes because it was more business and being in the right place and all that. But that one comes to mind.
Joey La Motta lost to a guy named Raadik. His famous brother Jake avenged the loss a few months later
The Klitschkos were so honourable that one always tried to avenge their brother's loss. They did that by trying to force opponents to sign contracts where the opponent would be tied into fighting the brother. Great guys. Currently saving Ukraine from their penthouse too.
That's how we speak? He didn't knock him out, he stopped him on cuts with Puritty still coming forward, Puritty definitely would've made it all 12.....but yeah a stoppage is a stoppage.