This is a reversal clue - look for indicators like 'back', 'returned', 'up' (in down clues), or 'west' (in across clues)
Reverse the letters of a word from the clue
Answer: ATROPHIED | Definition: 'degenerate' | Wordplay: A charade of A (‘active’) plus TROP, a reversal (‘regressed’) of PORT (‘harbour’) plus HIED (‘moved fast’).