Shane Greene is the closer of the Detroit Tigers. After a failed venture at starting for the Yankees (and Tigers, at first), they decided to transition him to the bullpen. After struggling with that at first, he was successful in 2017, which was his first full season in the bullpen.
In 2017, he pitched in 71 games and had an ERA of 2.66 with 9 saves. He struck out nearly 10 batters per nine innings but walked 4.5 per nine innings as well (which is a bit high).
He has an ERA of 4.15 in 2018 (which went up from 3.38 before last night). However, he is walking less than 2.5 per nine innings compared to 10.4 strikeouts.
Greene is a free agent after the 2020 season so he would also have some team control after this season.
Kelvin Herrera has been excellent this season for the Royals. He is their closer and he has been, virtually, the only bright spot.
He has an ERA of 0.76 this year with a FIP of 1.97. Additionally, he has 13 saves and in 23 2/3 innings he has walked exactly zero batters. Zero. He is averaging just under 8 strikeouts per nine innings.
In the past six seasons, he has averaged 69 appearances a season with a 2.81 ERA.
The two-time All Star also won a World Series with the Royals in 2015 and was excellent in the playoffs in general. In 22 games, he had an ERA of 1.22 and he has struck out nearly 12 per nine innings in postseason play.
It should also be noted that he was teammates with current Rockies closer Wade Davis and his bullpen coach was current Rockies pitching coach Steve Foster was the team’s bullpen coach through 2012 and was a special assistant with the team until he came to the Rockies.