Shock as river gets into reconstructed Metro (6)
I believe the answer is:
tremor
'shock' is the definition.
(I have seen 'Small shock ' mean 'tremor' so perhaps 'shock' could also mean 'tremor')
'river gets into reconstructed metro' is the wordplay.
'river' becomes 'r' (abbreviation).
'gets into' is an insertion indicator.
'reconstructed' indicates anagramming the letters.
'metro' is an anagram of 'temor'.
'r' placed within 'temor' is 'TREMOR'.
'as' is the link.
(Other definitions for tremor that I've seen before include "Quivering" , "Involuntary quiver" , "Strong shake" , "Slight earthquake" , "Vibration from earthquake" .)