According to NASM’s sports performance training manual “endurance athletes are generally recommended to ingest 1.2-1.4 g/kg/day.”
The manual also highlights that “sports performance professionals need to be aware that the need for protein may be higher during the first 3-6 months of training when muscle hypertrophy rates are accelerated.”
The NSCA’s Essentials of Personal Training, second edition, states that
“a general recommendation for athletes is 1.2 to 2.0 g/kg per day depending on sport, training intensity, total caloric intake, and overall health(pg.113)” They also say that protein requirements are higher than average for those on calorie or animal protein restricted diets.
According to ACE’s LWMC (now Health Coach) manual, the protein requirements for an endurance athlete are 1.2-1.4 grams of protein per kilogram of body weight per day. The protein requirements for a strength and conditioning athlete may need up to 1.6-1.7 grams of protein per kilogram of body weight per day. (ADA, 2000)
I have heard of all the answers already posted.
I will add that scientific information says that 0.8 g/kg protein per day is probably enough for athletes as well as the general public (IOM Food and Energy Board, 2005). This amount is the minimum, not necessarily the ideal or maximum.
Once more, it seems that nutrition is still under debate.