Crowd proverbially there erupted (5)
I believe the answer is:
three
'crowd proverbially' is the definition.
(I've seen this in another clue)
'there erupted' is the wordplay.
'erupted' indicates an anagram (I've seen 'erupts' mean this).
'there' with letters rearranged gives 'THREE'.
(Other definitions for three that I've seen before include "One, one, one" , "Number of blind mice" , "A crowd, you might say" , "Number of strikes before you're out" , "Number constituting a crowd?" .)