2021 is Andrew Mitchel's first year with the ThunderBolts and first as a professional. He signed as a free agent on April 13, 2021. He was selected in the eighth round of the 2019 amateur draft by the San Diego Padres but did not pitch in the Padres organization.

Andrew attended San Jose State University, where he pitched for two years. In his first season with the Spartans, as a junior, he was named the Mountain West's Co-Pitcher of the Year, going 6-2 with a 3.72 ERA and 101 strikeouts in 87 innings pitched. Overall, he struck out 213 hitters over 171.2 innings with a 4.14 ERA in 33 career appearances at San Jose State. He also spent single seasons at Grossmont College and Fresno City College, going a combined 8-2 with a 3.51 ERA at those two stops. Mitchel attended Buhach Colony High School in Atwater, California.