Stupidly gamble about a pound in sport (4,4)
I believe the answer is:
ball game
'sport' is the definition.
(ball game is a kind of sport)
'stupidly gamble about a pound' is the wordplay.
'stupidly' indicates an anagram.
'about' indicates putting letters inside.
'pound' becomes 'l'.
'gamble' with letters rearranged gives 'blgame'.
'a'+'l'='al'
'blgame' enclosing 'al' is 'BALL GAME'.
'in' acts as a link.
(Other definitions for ball game that I've seen before include "Eg, tennis or rugby" , "Tennis or hurling, for example" , "A sport such as soccer, rugby, cricket, hockey etc" , "squash, perhaps?" , "soccer, for example" .)