Piatnik was selected in the eighth round of the 2015 draft by the Reds out of State College of Florida-Manatee. He had signed to play the following season at LSU, but the Reds convinced Piatnik to sign instead. In college Piatnik was a smooth-fielding shortstop with some speed. The defense has carried over into professional ball, but as an outfielder. He also stole 10 bases with short-season Billings in 2015. After starting the 2016 season on the Billings roster, Piatnik advanced to Low-A Dayton.