Players, being experts, restricting lock (9)
I believe the answer is:
actresses
'players' is the definition.
(actress is a kind of player)
'experts restricting lock' is the wordplay.
'experts' becomes 'aces' (ace is a kind of expert).
'restricting' means one lot of letters goes inside another.
'lock' becomes 'tress' (I've seen this before).
'aces' enclosing 'tress' is 'ACTRESSES'.
'being' acts as a link.
(Other definitions for actresses that I've seen before include "Female impersonators" , "Female thespians" , "Female performers" , "Starlets" , "Stage performers" .)