Having left for a run, run smoothly, getting a stitch (4)
I believe the answer is:
purl
'stitch' is the definition.
(purl is a kind of stitch)
'having left' is the wordplay.
'having' becomes 'pur' (I can't explain this - if you can you should believe this answer much more).
'left' becomes 'l' (common abbreviation).
'pur'+'l'='PURL'
'for a run run smoothly getting a' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for purl that I've seen before include "form loop" , "Twisted gold wire" , "Knitting stitch type" .)