Felix Sturm retained the WBA middleweight title Friday night after fellow German Sebastian Zbik retired before the 10th round at the Lanxess Arena.
Zbik made the better start but appeared to tire midway through the bout, with the defending champion looking fresher despite taking some heavy blows.
Sturm had Zbik clearly troubled at the end of the ninth round, with American referee Raul Caiz Sr., asking the challenger if he could continue.
Though the 30-year-old Zbik insisted he could, his corner felt otherwise and Caiz ended the fight before the next round could start.