The SD mindset is utterly vital because it is one of the primary roots and fonts for excellent achievement and quality character for human beings regardless of the culture,gender,age and challenges that life throws at us,in whatever venue. The difference between the SD mindset and the sports mindset is that the sportive mindset is the range and depth of stimuli: the sportive mindset's stimuli peaks at about half of the intensity level of the SD mindset. This difference oftentimes has a direct impact on one's performance and character quality throughout one's entire life. Both the SD and sport mindset take execise,health,discipline,respect,family and more to very very high levels,if done properly...so both sport and SD mindsets encompass the laudable activities that you mention.
Personally, I don't see any difference between the "sportive" mindset and the "SD" mindset. If anything, I think it is easier to defend yourself against the normal situation (like your son's, weak kids with weak skills trying to assert themselves) than competition, because the higher you go, the harder it is.