Individuals who suffer from sicke cell anemia have deformed erythrocytes. The parasite that causes malaria(plasmodium malarie) uses erythrocytes for reproduction and as part of the infection. Those parasites can't infect sickle erythrocytes. It supports evolution by natural selection because individuals who had sickle cell couldn't get malaria so they lived long enough to have offspring and pass on their genes(including sickle cell). Individuals who didn't have sickle cell died of malaria and didn't get to have offspring. That's why sickle cell has a high frequency in the continent of Africa where malaria is also frequent.
