Wager about reserve in stock exchange, with prices falling? (4,6)
I believe the answer is:
bear market
'stock exchange with prices falling?' is the definition.
'wager about reserve' is the wordplay.
'wager' becomes 'bet' ('bet' can be a synonym of 'wager').
'about' means one lot of letters goes inside another.
'reserve' becomes 'earmark' ('earmark' can be a synonym of 'reserve'**).
'bet' placed around 'earmark' is 'BEAR MARKET'.
'in' acts as a link.
(Other definitions for bear market that I've seen before include "Situation where there are more sellers than willing buyers" , "prices low in this" , "when stock prices fall" , "Situation with falling share prices" .)