To me, sports car are cars that are track-orientated. They don't need to be hard edged, but have features that give it an advantage on track. It could be handling, power, weight. So in this category, the M3, MX-5, Type R, NSX, 911, Ferraris except for the 550/575, Skyline, and even the lowly Mini Cooper S (John Works version) qualify.
Unfortunately, the Civic sports is not a sports car to me. But it is a sporty car. Now, if Honda went and gave it suspension that was specially tuned for the track like the Type R's, then I'd put it into the sports car category.
