Michael Mateja is in his first season with the ThunderBolts and second as a professional. He signed on August 6, 2019. Mateja's pro career began when he was selected in the 25th round of the 2018 Amateur Entry Draft. He spent parts of two seasons in the Braves' organization, reaching as high as Class A Rome and hitting .283 overall with a .405 on-base percentage over 62 games. He played for three years at North Central College and hit .396 there, including .444 as a junior in 2018. He was a two-time Division III All-American and was twice named the College Conference of Illinois and Wisconsin Player of the Year. Michael attended Bradley-Bourbonnais Community High School in Bradley, Illinois.