What high school classes do I need to take to become a sports scientist?

You could take subjects at school that "might" help, but it doesnt really matter, not unless a university specially requores it (if you wanted to be a maths teacher the University may require you to have grades in math) its what you do at university that counts. Find out what you will need to study at university and find out how many and what school grades the university requires.It will probably demand you have grades in science and Physical education, but 2 grades isn;t enough, they will probably require another 2, but they wont demand them to be anything, so you could do music and art, something you enjoy, as long as you have whatever number of grades they require.

Take lots of science and math classes. Try to get as far ahead in those areas without falling behind in any other subjects.