§ 02 · King James Bible
Genesis 38:9
And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother’s wife, that he spilled it on the ground, lest that he should give seed to his brother.
Simple English
Onan understood that the sperm was not supposed to be his; whenever he had sex with his brother's wife, he released it onto the ground instead, so as not to have children for his brother.
* Work in progress - there may be occasional inaccuracies