1. unskilled or untrained for one’s work; amateur:
a jackleg electrician.
2. unscrupulous or without the accepted standards of one’s profession:
a jackleg lawyer.
3. makeshift; temporary.
4. an unskilled or unscrupulous itinerant worker or practitioner.
1840–50, Americanism; perhaps jack1+ (black)leg
“Out there in the sunshine the jackleg looked the part, so I wondered how we come to be faked by him.“
-Herbert Quick, Yellowstone Nights