A crowd, they say, dispersed there (5)
I believe the answer is:
three
'a crowd they say' is the definition.
(ref to the phrase 'two's company, three's a crowd')
'dispersed there' is the wordplay.
'dispersed' is an anagram indicator.
'there' is an anagram of 'THREE'.
(Other definitions for three that I've seen before include "Prime number" , "Number of feet in a yard" , "One, one, one" , "There (anag.)" , "A crowd, you might say" .)