Open lock swimming in a piece of clothing (4-4)
I believe the answer is:
polo-neck
'piece of clothing' is the definition.
'polo neck' can be an answer for 'clothing' (I've seen this before). I'm not sure about the 'piece of' bit.
'open lock swimming' is the wordplay.
'swimming' is an anagram indicator.
'open'+'lock'='openlock'
'openlock' anagrammed gives 'POLO-NECK'.
'in a' is the link.
Can you help me to learn more?
(Other definitions for polo-neck that I've seen before include "Style of sweater collar" , "Pullover, high turned collar" , "High close-fitting collar" , "A high turned-over collar on a jumper" , "Type of sweater collar" .)