Ok, I will throw my 2 cents on this one. Qualifications are 17 years auto repair on English and German autos 1968-1985, Certified Journeyman rated mechanic.
A sports car is a two seat fixed or drop head coupe. In america that woud be a two seat hard top or convertable.
Examples: not inclusive

MG Midget, MGA, MGB, MGC
Triumph TR6, TR4, TR3, Spitfire, Stag
Austin/Healy 3000, sprite
Sunbeam Tiger
Morgan +4
Jaguar E-type
Porsche 356,911,912
Volkswagen 914-4, 914-6
Chevrolete Corvette
Ford, early Thunderbird
Any vehicle with more then 2 real seats, could be a sports sedan whether two doors or four. An example of this would be the Mini Cooper or MG 1100 and the Triumph 2000. SCCA classes not withstanding, this would be a general laymans clasification.

Oh for the days long gone of real sports cars,