Young adult novels typically have a protagonist that the reader can identify with. If the protagonist has expertise in something (in this case, he's a fifteen year old outstanding hockey player) does that become a problem with regards to the reader identifying with him?
I don't like sports but I can always relate to someone who has found something they enjoy and can express a talent in. As long as you bring that out in the story along with all the hockey phrases the reader might not know, the reader will be able to identify with the character and learn something as well. Make it exciting. I remember reading about a character oil painting when I was younger and afterwards I had to give it a try.
Hockey player or not, he is still a teen with all the tonnage that comes with the period. And that, people will identify with.
No, in fact, one of the best ways to get me (and readers in general) to identify with a character is to give that character something to care about and be good at.
It doesn't matter as long as that person isn't super-good at everything and beyond flaws. That's why Superman is generally seen as the least identifiable comic book character, because he has far fewer flaws than, say, Batman or Spider Man. I've heard this phrased as a three pronged sliding scale - the three prongs being character sympathy, character competence, and character proactivity. You only have a problem with identification if you max out (or zero out) all three at once. Your character has competence in an area - so either make them less competent elsewhere or add compensation in the sympathy or proactivity scales.
On the contrary, I think having things that make that character unique is quite important for a lot of readers. If they have enthusiasm for something, the reader can usually understand enough to relate to their feelings. When I was about 15 I read a book about a girl who adored running. At the time I hated all forms of exercise, but it made her more 'her', and I liked how committed she was. She used it to calm her down, sometimes went running with a friend, had a friend who hated it but cycled next to her yelling support while she was in a race... all of these things were easy to understand and relate to, and added interest to the story. While she was great at running, she had doubts and periods where she completely slacked and felt like all her dreams would die - which also, for me, added some humour/fear/understanding on behalf of the reader.
