The reason for being announced ineligible was due to him failing his entrance exams such as the SAT/ACT.
Per 11W:
"Ross was ranked as the 43rd best player in the class of 2011 by Rivals and as the 13th best small forward in the class by Scout. Ross' agenda in the short term appear to be to head back home to Mississippi in order to take a class and retake the SAT in an effort to be granted eligibility. Even without the talented freshman, the Bucks are still expected to be amongst the nation's premiere teams in 2011/2012. Ohio State still welcomes in the highly touted Amir Williams, Sam Thompson, Shannon Scott, and Trey McDonald to join a core that includes Jared Sullinger, Aaron Craft, and William Buford."