Since he was very good at using his skills with an axe and a sword, he volunteered to be in the Games. It's later known that he became a very formidable tribute that year, gaining a massive amount of sponsors.
After killing many tributes in the bloodbath, he allies with the Careers. Thorburn describes his Games in detail in, "The 40th Hunger Games." In the bloodbath, Raff killed three tributes, one from District 5. Later in the Games, there were mosquito mutts that were very lethal. The only way you could get them away from you was getting a bottle of bug spray you received from the cornucopia. These mutts later killed the pair from 8. It's also mentioned how Raff's district partner was very whiney over killing people, so when she didn't expect it, he killed her. Not much is known after this point in time.
After Raff wins, he later becomes friends with Mags Flanagan.