At draughts, he's twice the man he was (4)
I believe the answer is:
king
'he was' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'at draughts he's twice the man' is the wordplay.
'at' says to put letters next to each other.
'draughts he's twice' becomes 'ing' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'the man' becomes 'k' (abbreviation for king, a chess man).
'ing' after 'k' is 'KING'.
Can you help me to learn more?
(Other definitions for king that I've seen before include "Chess piece" , "Eponymous giant ape in movie" , "Card, draughts piece" , "Most important chesspiece" , "Man with a crown" .)