The stomach; a term used by boxers. I took him a punch in his bread basket; i.e. I gave him a blow in the stomach.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Bread * Breast FleetNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes