Eubank/ Watson and Benn/McClellan always spring to mind. Paul Ingle losing his last fighting and being sent to an early retirement was also pretty sad. Recently, watching Maccarinelli getting KO'd again wasn't too nice.
Lewis-Tyson should have been mentioned. :verysad Tyson was beyond shot & a stone overweight, with only a single round of stamina in him. If the fight had happened 2 years previously, Tyson would have gave Lewis a tough challenge, rather than being a mere human heavybag. Why exactly did Botha deserve a title shot in 2000? Tyson sparked him out back in '99.
Greg page, once a champion and top-notch fighter, being reduced to a $1500 purse journeyman and getting ko'd by someone like Dale crowe.
Not as bad obviously as a fatality, which are genuine sad moments for boxing, but my heart really went out to colin jones when the doctor called an end to his challenge for don curry's title. The guy dropped his head onto the corner rope and was inconsolable. The doc made the right call as his nose was split open like a fish's mouth.