At first, performance by hybrid yacht is variable (6)
I believe the answer is:
patchy
'is variable' is the definition.
(thesaurus)
'at first performance by hybrid yacht' is the wordplay.
'at first' indicates taking the first letters.
'by' says to put letters next to each other.
'hybrid' indicates anagramming the letters (I've seen this in other clues).
The initial letter of 'performance' is 'p'.
'yacht' with letters rearranged gives 'atchy'.
'p'+'atchy'='PATCHY'
(Other definitions for patchy that I've seen before include "Intermittent" , "Uneven in quality; showing signs of repair" , "Irregular in quality" , "Uneven in quality like repaired clothes" , "in an irregular way" .)