Coach finds one set of cards has every other heart missing (6-6)
I believe the answer is:
single-decker
'coach finds one set of cards has every other heart missing' is the definition.
I can't tell whether this definition defines the answer.
'coach finds one set of cards has every other heart' is the wordplay.
'coach finds' becomes 'single' (I can't justify this - if you can you should give a lot more credence to this answer).
'one set of cards' becomes 'deck' (I've seen this before).
'has' is a charade indicator (letters next to each other).
'every other' means one should take alternating letters (every other letter).
The alternating letters of 'heart' are 'er'.
'single'+'deck'+'er'='SINGLE-DECKER'
Can you help me to learn more?
(Other definitions for single-decker that I've seen before include "7" , "Type of bus" .)