Crutcher, Chris (1995) Ironman. New York: HarperCollins.
Plus, there is something awesome about a rabbit in samurai armor.
And yes, you are right. This book is maybe a stretch in terms of being related to sports. But I would encourage you to read it and correct me if I am wrong, but Usagi’s system of honor looks to me an awful lot like good sportsmanship. These books could be read by a middle school phys ed class and would lead to a great discussion of sportsmanship that goes beyond the usual lip service it receives.
These books would be ideal for fourth grade and up. These is some violence here, but nothing gory. In a couple of the stories, Usagi does drink Saki (wine), but never to excess and he seems to usually prefer tea. Sometimes the bad guys are shown to be drunk, but the story dose not dwell on it.