They're talking about individual athlete, as in coming back from injury, or cancer, not teams coming back from behind.
Tommy John....
Individual? Ok, then, Ben Hogan hands down! Almost killed in a car crash, he spent months in the hospital and could barely walk for a year. He started his recovery by walking across his living room, then his yard, then his neighborhood. When he didn't come home his wife would get in the car and go find him as he would be somewhere unable to move any farther. He went on to win two more US Opens and a British. He probably would have won the Grand Slam but in those days there was actually a scheduling conflict between the PGA and the British and transoceanic flights were still not the norm. And that was in the day when you had to play 36 holes on Saturday. Hogan's legs never fully recovered, he had to soak them for long periods after every round.