Following cart gets upset over court card (8)
I believe the answer is:
tracking
'following' is the definition.
(I know that tracking is a type of following)
'cart gets upset over court card' is the wordplay.
'gets upset' is a reversal indicator (I've seen 'getting upset' mean this).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'court card' becomes 'king' (king is a kind of court card).
'cart' backwards is 'trac'.
'trac'+'king'='TRACKING'
(Other definitions for tracking that I've seen before include "Following the trail of" , "Following progress of" , "Following (groove in record)" .)