He advanced to the finals in the men's 400 meters race at the 1908 Summer Olympics after winning his preliminary heat with a time of 49.8 seconds and his semifinal in 49.4 seconds. In the first running of the final race, Carpenter came in first out of the four runners, clocking 47,8 seconds. However, umpire Roscoe Badger determined that Carpenter had willfully interfered with British runner Wyndham Halswelle. Though the obstructing maneuver was then legal under American rules, the Olympic contests were held under British rules, which did not allow it. Carpenter was disqualified and the race was ordered to be repeated without him. His countrymen, John Taylor and William Robbins, protested the ruling by boycotting the second final, leaving Halswelle to take the gold medal uncontested in the only walkover in the modern Olympic history.