Went back to find nice surprise in grass (9)
I believe the answer is:
retreated
'went back' is the definition.
('retreat' can be a synonym of 'go back')
'nice surprise in grass' is the wordplay.
'nice surprise' becomes 'treat' (I've seen this before).
'in' means one lot of letters goes inside another.
'grass' becomes 'reed' (type of grass plant).
'treat' going inside 'reed' is 'RETREATED'.
'to find' is the link.
(Other definitions for retreated that I've seen before include "pulled back" , "Retired" , "Went back" , "given extra medical care?" , "Left" .)