Ah yeah, you probably shouldn't be including a .c file. The makefile compiles sprites.c separately, so essentially you are including the sprites.c code twice in the whole project. If you really want to include code, make it a .h file or something.
Edit:
After taking a closer look at the Makefile, I suppose it'll only compile sprite.c separately if you have sprite.o after OBJS in the Makefile. I might be wrong, though.