General answer found in Mark Chapter 9? (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A(abbrev. for “answer”) contained in ( in ) [ M(abbrev. for “mark”) + C(abbrev. for “chapter”, one of the parts/divisiona in a book) + ARTHUR(first name of Ashe, the tennis player in 9 across) ].