How is this as a large definition of a sport car:

A sport car is a vehicle that offers superior performance, handling and drive feel that entices you to (safely) push it to the limit for fun on a public road or at the track.

I like that one, but feel this one is too restrictive:

A sport car is a vehicle that is purpose built for going fast on a public road or at the track compromising on other considerations like confort and practicality.