Lay a rug, with regret, the wrong way round (7)
I believe the answer is:
amateur
'lay' is the definition.
('amateur' can be similar in meaning to 'lay')
'a rug with regret the wrong way round' is the wordplay.
'rug' becomes 'mat' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'regret' becomes 'rue' ('rue' can be a synonym of 'regret').
'the wrong way round' is a reversal indicator.
'rue' back-to-front is 'eur'.
'a'+'mat'+'eur'='AMATEUR'
(Other definitions for amateur that I've seen before include "Fancier" , "Unpaid practitioner" , "He's not professional" , "Inept, non-professional" , "enthusiast" .)