Struck with top of southpaw’s boxing glove (7)
I believe the answer is:
smitten
'struck with' is the definition.
'top of southpaw's boxing glove' is the wordplay.
'top of' says to take the initial letters.
'boxing glove' becomes 'mitten' (I've seen this before).
The first letter of 'southpaw' is 's'.
's'+'mitten'='SMITTEN'
(Other definitions for smitten that I've seen before include "Infatuated with mittens" , "Much affected; struck" , "Much taken by" , "Struck (by love?)" , "Head over heels in love" .)