Most sports cars are recognized by larger engines, which make cars go faster. Speed equals cost in the insurance business.
While innovations continue in the ongoing push to make sports car safer, they are simply not rigged with the safety nets ordinary cars are. The smaller size of a sports car also contributes to accident/injury risk.
Two doors are traditionally associated with sports cars.
You can have an ordinary car, but if you add on a spoiler or settle for a convertible type, you will be entering the sports car realm.
Contrary to popular belief, the color red alone will not impact your insurance in a negative way, even though it's associated with fast cars. Rather, bright colors can be insurance savers as they are considered easier to spot on the road, therefore, have less chance of collision; however, a red car with sports features is well, ah, a sports car.