Hunter x Hunter wouldn't be my choice for fight genre - if you're going with a fight genre, you'd need Dragonball Z, since I think that's the standard. If you want a Togashi piece, YYH is much more classic than H x H (and borrows a lot of the tournament-style that you might . Still, none of those strike me as true "sports" manga - although they are all shonen.

I can't think of any other "sports" manga that Obata did - as far as I'm aware, he did Ayasuri Sakon, Hikago, and Death Note (all different genres although there's a lot of similarities in the characters).

Dan Doh is another example of weird sports animes - welcome to the wonderful world of golf.

Although it's not "shonen," Yawara should be mentioned as an important piece of sports anime.