Oxford college chaps full of silly rot (6)
I believe the answer is:
merton
'oxford college' is the definition.
(I've seen this before)
'chaps full of silly rot' is the wordplay.
'chaps' becomes 'men' (chap means a man).
'full of' indicates putting letters inside.
'silly' is an anagram indicator.
'rot' is an anagram of 'rto'.
'men' placed around 'rto' is 'MERTON'.
(Other definitions for merton that I've seen before include "Comic" , "Oxford college: London borough" .)