For the Tigers, it's a low-risk, high-reward move.
Rosenthall, once one of the most dominant relievers in baseball, underwent Tommy John surgery in 2018 and hasn't been the same since.
He was released by the Nationals this week after a 12-game stint that saw him allow 16 earned runs.
At his best, Rosenthal saved 93 games for the Cardinals from 2014-15. He posted a 2.65 ERA and well more than a strikeout per inning during that span. He was an All-Star and garnered Cy Young votes in 2015.
If the Tigers can help him rediscover his touch, they could try to flip him at the trade deadline next month. Rosenthal still throws extremely hard, with a fastball that can hit triple digits, but his control has abandoned him this year.
The right-hander is still just 29 years old.