Struck, firstly slapped with glove (7)
I believe the answer is:
smitten
'struck' is the definition.
(synonyms)
'firstly slapped with glove' is the wordplay.
'firstly' indicates taking the first letters.
'with' means one lot of letters go next to another.
'glove' becomes 'mitten' (mitten is a kind of glove).
The first letter of 'slapped' is 's'.
's'+'mitten'='SMITTEN'
(Other definitions for smitten that I've seen before include "Hit (by remorse, love)" , "Obsessed (when in love?)" , "Very much in love" , "Much taken by" , "Enchanted by mittens" .)