Customs that suit many horsemen (6,6)
I believe the answer is:
riding habits
'many horsemen' is the definition.
Although both the answer and definition are plural nouns, I can't understand how one could define the other.
'customs that suit' is the wordplay.
I cannot really see how this works, but
'customs' could be 'habits' (habit is a kind of custom) and 'habits' is found within the answer.
The remaining letters 'riding' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for riding habits that I've seen is " suit the mounted".)