Zack Britton debuted for the Baltimore Orioles in 2011 and began his career as a middle reliever. Although he pitched well, he wasn't particularly outstanding. However, in 2014, he unexpectedly worked his way into the closing role and converted 37 of 41 save opportunities. This helped the O's make the playoffs, and Britton finished the year with a 1.65 ERA and a 0.904 WHIP.

In 2015, Britton continued to improve and made his first All-Star Game appearance. He recorded 36 saves with a 1.92 ERA and a 0.990 WHIP. However, 2016 was the best year of his career. Britton led the AL in saves (47) and games finished (63) and was nearly untouchable with a 0.54 ERA and a WHIP of 0.836. He was an All-Star again and won The Sporting News Pitcher of the Year award, finishing fourth in Cy Young voting.

Although he started strong in 2017, Britton began to deal with injuries, including an Achilles tear that put him on the disabled list to start the 2018 season. By this time, the Orioles were no longer competitive, and Britton was eventually traded to AL East rival, the New York Yankees. While he was no longer the closer, he still performed well in 2019 and 2020 with ERAs under two.

Unfortunately, bone chips and Tommy John surgery in 2021 led to his downfall, and he retired after the 2022 season with 154 career saves. Nonetheless, for a brief time, Zack Britton was the top relief pitcher in the American League, and his outstanding bullpen campaign during his time with the Orioles will be remembered as one of the best in franchise history.