To hit below the belt. To strike unfairly. It is prohibited in prize-fighting to hit below the waistbelt. 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 man's 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.