Wager club's regularly taken up during contest (6)
I believe the answer is:
gamble
'wager' is the definition.
(I know that wager is a more specific form of gamble)
'club's regularly taken up during contest' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'taken up' is a reversal indicator.
'during' is an insertion indicator.
'contest' becomes 'game' (game is a kind of contest).
The alternating letters of 'clubs' are 'lb'.
'lb' reversed gives 'bl'.
'bl' going within 'game' is 'GAMBLE'.
(Other definitions for gamble that I've seen before include "Bet money" , "Flutter" , "Take a chance, speculate" , "back" , "Risky enterprise" .)