"Apparently, "to kick against the goads" was a common expression found in both Greek and Latin literature—a rural image, which rose from the practice of farmers goading their oxen in the fields. Though unfamiliar to us, everyone in that day understood its meaning.
Goads were typically made from slender pieces of timber, blunt on one end and pointed on the other. Farmers used the pointed end to urge a stubborn ox into motion. Occasionally, the beast would kick at the goad. The more the ox kicked, the more likely the goad would stab into the flesh of its leg, causing greater pain."
Src: http://www.jesus.org/early-church-history/the-apostle-paul/h...