Recidivist regularly concealed gear under rugby player's top (10)

'recidivist' is the definition.
(synonyms)

'regularly concealed gear under rugby player's top' is the wordplay.
'regularly concealed' means one should take alternating letters (letters removed at regular intervals).
'under' says to put letters next to each other (below, in a down clue).
'rugby player's' becomes 'back's' (type of rugby player).
'top' becomes 'lid' (lid is a kind of top).
The alternating letters of 'gear' are 'er'.
'backs'+'lid'='backslid'
'er' after 'backslid' is 'BACKSLIDER'.