Mark's wild rage during a race (6)
I believe the answer is:
target
'mark's' is the definition.
(synonyms)
'wild rage during a race' is the wordplay.
'wild' indicates anagramming the letters.
'during' is an insertion indicator.
'a race' becomes 'tt' ().
'rage' anagrammed gives 'arge'.
'arge' inserted within 'tt' is 'TARGET'.
(Other definitions for target that I've seen before include "Object to be attained by archers (or fund raisers?)" , "Point to aim at (6)." , "'Aim, goal (6)'" , "aunt Sally" , "A result to aim at" .)