Spare tyre short of a blow (5)
I believe the answer is:
punch
'blow' is the definition.
(I know that punch is a type of blow)
'spare tyre short of a' is the wordplay.
'spare tyre' becomes 'paunch' (I've seen this before).
'short of' indicates named letters should be taken away.
'paunch' with 'a' taken away is 'PUNCH'.
(Other definitions for punch that I've seen before include "Hit with a fist" , "Alcoholic fruit drink" , "Hit - party drink" , "Magazine of yesteryear" , "Wife-beater" .)