Yes, many ED applicants are athletes. That being said, applying ED will increase your chances - but not as dramatically as the ED acceptance rate may seem. I have been told this by my guidance councilor. She told me that is why UPENN’s ED rate is so large. I am assuming this is similar to Williams.
Also, some colleges will only recognize legacy status (UPENN) if you apply ED. So this will also dramatically increase the ED acceptance.
Chance me?
http://talk.collegeconfidential.com/what-my-chances/1903457-chance-me-will-chance-back.html#latest