Why are spoilers placed at the back of some sports cars?

Answer 1

Sports car's have powerful engines . So if the engine it attached to the front wheels then front wheel's would have to the acceleration as well as the steering which would spoil the handling especially during turning fast (the reason front engine car screech during turing fast).

Now putting the engine at the back and connecting it to the rear wheels , the rear wheels would do the job of accelerating , and the front wheels would be free to do the steering part .

Answer 2

Some are just for looks, but some are functional. The function they are used for is to create down pressure on rear axle for traction purposes at high speed. When you drive at higher speeds, the air being directed over the car by aerodynamics would then hit the spoiler wing and push down on rear of car giving them more traction and control, especially if it rear wheel drive.