In the event, an equestrian garment? (6)
I believe the answer is:
jumper
'equestrian garment?' is the definition.
'jumper' can be an answer for 'garment?' (jumper is a kind of garment). I am unsure of the 'equestrian' bit.
'in the event an' is the wordplay.
'in the event' becomes 'jum' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'an' becomes 'per' (synonymous as in 'once an hour', 'once per hour').
'jum'+'per'='JUMPER'
Can you help me to learn more?
(Other definitions for jumper that I've seen before include "Kangaroo and knitted garment" , "Knitwear - bounder" , "field athlete" , "Top" , "that may be long for an athlete" .)