E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To hit below the belt. To strike unfairly. It is prohibited in prize-fighting to hit below the waist-belt.
To call men knaves and fools, to charge a man with nepotism, to make a slanderous report which is not actionable, indeed to take away a mans character in any way where self-defence is impossible, is hitting him below the belt.
Lord Salisbury hits hard, but never hits below the belt.Daily Telegraph, November, 1885.
To hold the belt. To be the champion. In pugilism, etc., a belt is passed on to the champion.