Hole in the wall? Collect stake money on the way back (4)
I believe the answer is:
loop
'hole in the wall?' is the definition.
(loop can mean an arrow slit in a medieval wall)
'collect stake money on the way back' is the wordplay.
'collect stake money' becomes 'pool' (pool can mean to collect money for a fund).
'on the way back' says the letters should be written backwards.
'pool' in reverse letter order is 'LOOP'.
(Other definitions for loop that I've seen before include "Shape produced by a curve crossing itself" , "Branch line" , "Oval or U-shaped coil or bend" , "Shape formed by a closed curve that does not intersect itself" , "Curve that bends round and crosses itself" .)