Socialist getting eccentric sign of dismissal (3,4)
I believe the answer is:
red card
'sign of dismissal' is the definition.
(I've seen this before)
'socialist getting eccentric' is the wordplay.
'socialist' becomes 'red' (socialism is often associated with the colour red).
'getting' says to put letters next to each other.
'eccentric' becomes 'card' (card can mean an eccentric person).
'red'+'card'='RED-CARD'
(Other definitions for red card that I've seen before include "maybe footballers would dispute it?" , "A player is shown it for a serious infringement" , "Sending off" , "Signal of dismissal" , "It signals a serious rule infringement" .)