Criticise disorderly rabble besieging old university (8)
I believe the answer is:
belabour
'criticise' is the definition.
(I've seen this before)
'disorderly rabble besieging old university' is the wordplay.
'disorderly' is an anagram indicator.
'besieging' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'university' becomes 'u' (abbreviation for university).
'rabble' anagrammed gives 'belabr'.
'o'+'u'='ou'
'belabr' placed around 'ou' is 'BELABOUR'.
(Other definitions for belabour that I've seen before include "Discuss (a point) excessively" , "discuss at length" , "thrash" , "censure" , "Attack physically or verbally" .)