Pennington sustained a right arm injury and has elected to retire, Todd Rosiak of the Milwaukee Journal Sentinel reports.
Pennington underwent Tommy John surgery coming out of high school and has since battled a slew of additional arm injuries. The 22-year-old was traded from the Red Sox to the Brewers along with Travis Shaw and Mauricio Dubon for Tyler Thornburg in 2016 and had an electric fastball, but he's pitched in only 32 minor-league games over the last three-plus seasons. Pennington revealed on his personal Instagram he is facing another Tommy John surgery, prompting his decision to retire.