Those you hold in response to a call for restraint? (6)
I believe the answer is:
horses
'those you hold in response' is the definition.
I can't tell whether this definition defines the answer.
'call for restraint?' is the wordplay.
I cannot quite see how this works, but
'call' could be 'ho' (historical exclamation used to attract attention) and 'ho' is located in the answer.
This explanation may well be incorrect...
'to a' is the link.
Can you help me to learn more?
(Other definitions for horses that I've seen before include "''If wishes were . . . . . ., beggars would ride''" , "Eg, stallions" , "Equine beasts" , "Hoofed mammals (which go with 19 4)" , "Equine animals" .)