Rat keeping tense and upright (8)
I believe the answer is:
standing
'upright' is the definition.
(I've seen this before)
'rat keeping tense and' is the wordplay.
'rat' becomes 'sing' (both can mean to inform on someone).
'keeping' is an insertion indicator.
'tense' becomes 't' (abbreviation used in many dictionaries).
't'+'and'='tand'
'sing' enclosing 'tand' is 'STANDING'.
(Other definitions for standing that I've seen before include "(Of corn) not yet reaped" , "Prestige" , "Status, reputation" , "Position or reputation" , "Social reputation" .)