Animals run out over grass at back of pasture (3,4)
I believe the answer is:
roe deer
'animals' is the definition.
(I've seen this before)
'run out over grass at back of pasture' is the wordplay.
'run out' becomes 'RO' (cricket abbreviation).
'over' shows that the letters should be reversed in order.
'grass' becomes 'reed' (type of grass plant).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'back of' indicates one should take the final letters.
The last letter of 'pasture' is 'e'.
'reed' in reverse letter order is 'deer'.
'deer' put after 'e' is 'edeer'.
'ro'+'edeer'='ROE-DEER'
(Other definitions for roe deer that I've seen before include "how beastly is this!" , "Small antlered animal(s)" , "Native wild animal" , "Small (antlered) mammal" , "Graceful animal with small antlers" .)