Run slowly, when let loose, round the haystack (7)
I believe the answer is:
trickle
'run slowly' is the definition.
'trickle' can be an answer for 'run' (trickling is a kind of running). I'm not certain of the 'slowly' bit.
'let loose round the haystack' is the wordplay.
'loose' is an anagram indicator (letters are loosened from their original positions).
'round' is an insertion indicator.
'the haystack' becomes 'rick' (synonyms).
'let' with letters rearranged gives 'tle'.
'tle' placed around 'rick' is 'TRICKLE'.
'when' acts as a link.
Can you help me to learn more?
(Other definitions for trickle that I've seen before include "Move slowly" , "A series of drops" , "Run in drops" , "Flow in a small stream" , "Flow in a slow thin stream" .)