Obscure flash in college yard (6)
I believe the answer is:
cloudy
'obscure' is the definition.
(I've seen this before)
'flash in college yard' is the wordplay.
'flash' becomes 'loud' ('loud' can be a synonym of 'flash'**).
'in' means one lot of letters goes inside another.
'college' becomes 'c'.
'yard' becomes 'y'.
'c'+'y'='cy'
'loud' going inside 'cy' is 'CLOUDY'.
(Other definitions for cloudy that I've seen before include "Blurred" , "Dull, overcast" , "(Of a liquid) not clear" , "'Overcast, nebulous (6)'" , "Murky or nebulous" .)