how do you get this habit to stop? He definately does it when he is nervous/anxious, and he plays at a rep level in soccer and is doing it there. He says he likes playing and he says he isn't nervous, but today during the whole practice he was biting his finger nails!
My ds has gone through periods of nail-biting. The first round I resorted to bribery to get him to stop. He stopped for over a year. He's doing it again now. He's 7.5 years old. I'm not resorting to bribery again, but when I look at his little fingers I tell him that I love those little fingers so much and I wish he wouldn't bite them. I've also touched on some health issues since he bites the skin around them and frequently has small, open areas of skin. I'm not going to be too hard on him though. I constantly pick at my cuticles and skin around my fingers, so I figure the only thing I can do is tell him how I hate that I do that to my hands and that it makes me feel embarrassed sometimes.
There is also a polish that has a bad taste that your son might find helpful. I wanted to stop chewing my nails as a child so my mother got me some and the taste reminded me of my goal when I started chewing out of stress. He would need to be on board with this though and motivated to quit for it to work though IMO.
Sometimes biting (in the form of biting cheeks, lips or nails) can be a sign of food allergies. I was a nail biter my whole life until I was diagnosed and tested with food allergies and now I finally have nice non-biten nails. I'm sure it can also be a nervous bad habit but I thought the food allergy idea was worth mentioning.