Red card: did moan when sent off! (7)
I believe the answer is:
diamond
'red card' is the definition.
(I've seen this before)
'did moan when sent off' is the wordplay.
'did moan' anagrams to 'DIAMOND'.
Though, I am not sure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for diamond that I've seen before include "one of thirteen?" , "American pitch" , "60th anniversary" , "Very hard gem" , "Suit-baseball field - gem" .)