The rotten fellow tripped up! (6)
I believe the answer is:
fouled
'up' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'the rotten fellow tripped' is the wordplay.
I cannot really understand how this works, but
'fellow' could be 'ed' (short for Edward) and 'ed' is found within the answer.
The remaining letters 'foul' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for fouled that I've seen is " Soiled or broke the rules of the game".)