LapLap, in contrast to the niche interests that you listed (which may well gather a small but very devoted following in Japan), baseball is thoroughly mainstream. The fact that you don't have any baseball fans among your friends is actually a little surprising to me, but it may that there is some "selection bias" in your sample. Nonetheless, even among a crowd of non-sporty people, figures like Matsui and Ichiro are known cultural icons in a way that the world champion of yodelling or flamenco dancing simply isn't. So even if a kid isn't a passionate baseball fanatic, he's still likely to appreciate a baseball cap from America. I think you underestimate the cultural resonance that baseball has in Japan.