Seeing half of us in streetcar, a shock (6)
I believe the answer is:
trauma
'shock' is the definition.
(I've seen this before)
'seeing half of us in streetcar a' is the wordplay.
'seeing half of' indicates taking half.
'in' means one lot of letters goes inside another.
'streetcar' becomes 'tram' (synonyms).
'us' with half the letters taken is 'u'.
'u' put into 'tram' is 'traum'.
'traum'+'a'='TRAUMA'
(Other definitions for trauma that I've seen before include "Deep distress; injury" , "Emotional shock, long-lasting" , "dreadful shock!" , "Physical injury - powerful emotional shock" , "Severe shock, injury" .)