I read that "jock" means sports guy who is arrogant, stupid and only dates with cheerleaders, which has a negative image. In japan, sports-oriented people have a pretty good image like a hard worker, persistent, patient etc. I wonder if any expressions meaning sports-oriented person with such a good image exist. If any, please inform me.
I'm not from the US, so I can't really comment on the connotations of 'jock'. UrbanDictionary sheds some light on it though:
The others sort of follow that pattern. So, I think that jock does have some negative connotation. Creating stereotypes is never a good thing to do. As for something non-negative - athelete, sports enthusiast, sporty.To clear things up, there is a major difference between a jock and athletes. Jocks tend to abuse their popularity, while the athletes don't really mind who they talk to or hang out with.
Signs of a jock: Rude, arrogant, stupid, beats up people, dates only cheerleaders and hangs around other jocks
Signs of a true athlete: Love their sport, try to stay down-to-earth (a little arrogance is expected), hang out with whoever they want, date whoever they want, might beat people up but that doesn't mean it was uncalled for.
There is a fairly obscure word with nothing but positive connotations, but it's very rarely used: 'corinthian' - typically used in the collocation 'corinthian spirit'. Read more here: Amateur sports - Wikipedia, the free encyclopedia
The Corinthians were a football team (soccer) who were amateurs (gentlemen) who followed not just the letter but the spirit of sport: for instance if an opponent was injured, they would remove one of their own players to balance things out. If they conceded a penalty, then the goal keeper would make no attempt to save the free kick. There is still a Corinthian League. I think there are a lot of words for sportsmen that are positive, like champion and master, both of which are more than about winning and losing. Sportsmen refer to their behaviour as "professional", which means more than just being paid. The term Olympian is sporting, although it implies god-like. Victor Laudorum, is a latin term for worthy winner. In England, the word "Jock" is a slang term for Scotsman, and should be avoided
"Jock" is a slang term for "athlete" and does not necessarily suggest the person is not serious about his/her sport but a more refined term to refer to a person (male or female) who particpates in sports is "athlete".
The opposite of a jock would be a nerd.
Check out the early movies starring Patrick Dempsey for examples of these.
Another word for "jock" would simply be the dictionary word of athlete. That word may sound more suitable for describing a person who plays sports without the negativity that some perceive from jock.
"Jock" certainly does have a negative connotation, suggesting a person (exclusively male) who is recognized exclusively for his athletic prowess rather than for his intellectual abilities. The term derives from that protective accessory known as an "athletic supporter" (i.e., a jockstrap).
I don't know if there is a true opposite, though "nerd" does come close, being one who is exclusively intellectual (typically focused on a single discipline, such as computers), not at all athletic.
Jocks tend to believe they are universally admired. Nerds typically demonstrate a high degree of social ineptitude.
There are so many degrees of nerd. I was not at all athletic in high school, but neither would anyone call me a true nerd. Not at all interested in sports, I did well academically, but my focus was on my band. I found it humorous that those who ignored me and my bandmates because we weren't jocks would gladly pay admission to venues where we performed, even to the point of being "fans" (and the sole source of a good income for high school students of the day). Poetic justice, as it were.
In Great Britain "Jock" does not refer to an athlete, it is an American term. In Great Britain, "Jock" is used to refer to someone from Scotland and it is perfectly normal to use, just as Paddy is someone from Ireland and Taff someone from Wales, people from these countries also accept that these terms as the norm. For example when there is a Rugby or Football (soccer) match it's often used we're playing the Jocks.
Same as people from Great Britain refer to Americans as Yanks.
Hope this helps