"you" is not a letter -- it is a word! "U" is a letter and the word "uniform" is a school-related word that matches your question.
The generally accepted word for 'sport' was the same as for 'game' and 'school'. It is 'ludus'. It is a second declension noun.
The most popular sport in the world is football (soccer) football has mass amounts of fans in every continent on the planet and in most countries