What is a Jerkline Skinner?

A Jerkline Skinner is the main driver of a mule team who handles the reins. More precisely, he is the driver astride the neigh wheeler who handles a single line, the jerk line, that goes to the bit of the neigh leader. Pulling the line causes the leader to turn left. Jerking the line causes him to turn right.

The term skinner refers to a mule skinner, a person who drives mule teams.