One in regiment deployed for horsey event (4,7)
I believe the answer is:
race meeting
'horsey event' is the definition.
'race meeting' can be an answer for 'event' (race meeting is a kind of event). I'm not sure about the 'horsey' bit.
'one in regiment deployed' is the wordplay.
'one' becomes 'ace' (ace has a value of one in some card games).
'in' indicates putting letters inside.
'deployed' indicates anagramming the letters.
'regiment' anagrammed gives 'rmeeting'.
'ace' placed inside 'rmeeting' is 'RACE-MEETING'.
'for' is the link.
Can you help me to learn more?
(Other definitions for race meeting that I've seen before include "Aintree or Goodwood event?" , "Eg, sports event at Kempton Park" , "Sporting event with horses" , "A turf event" .)