What happened to the Pittsburgh Pirates' bullpen?

How did the Pirates' bullpen go from the best part of the team to one of the worst parts of the roster in such a short amount of time?
Apr 9, 2024; Pittsburgh, Pennsylvania, USA;  Pittsburgh Pirates pitcher David Bednar (51) surrenders
Apr 9, 2024; Pittsburgh, Pennsylvania, USA; Pittsburgh Pirates pitcher David Bednar (51) surrenders / Charles LeClaire-USA TODAY Sports

Many projected the Pittsburgh Pirates’ bullpen to be one of the best in baseball. It easily had the potential to be the best in the National League and top three in all of baseball heading into the year. But the pen hasn’t been nearly as good as everyone hoped it would be. They’ve given up a lot of close games, and have blown some leads, and it’s an adventure every time the Pirates turn to the pen. But what happened? How did this group once have so much potential to be arguably the weakest part of the team in such a short amount of time?

Injuries have definitely taken their toll on the bullpen. Losing Dauri Moreta in Spring Training was a massive blow to the pen. Moreta had an extremely promising 2023 breakout season, striking out a ton of batters and giving up very little hard contact. Moreta pitched 58 innings last year, with 34 coming in the 7th inning or later.

Ryan Borucki has also missed almost all of this year so far. The left-hander was an integral part of the Pirates bullpen in the second half of last year. He had just a 2.45 ERA, 3.50 FIP, and 0.74 WHIP while only allowing walks to 2.6% of opponents and holding them to an 85.7 MPH exit velocity. He ended 2023 with 16 straight scoreless innings. Borucki has been sidelined for all but 3.1 innings this year and doesn't have an ETA on his return.

Another integral part of the second half of the Pirates’ season was Carmen Mlodzinski. Mlodzinski had just a 2.25 ERA in his rookie year. By the end of the season, he was regularly getting playing time as a 7th/8th inning arm and even snuck some save opportunities in there too. He also was injured in Spring Training but was sent to Triple-A after his rehab. The Pirates have yet to recall him. He has struggled at Indy so far this year, but take minor league relief numbers with a grain of salt, especially this early into the year. Still, not having Mlodzinski has been a massive detriment.

The Pirates’ big off-season signing, Aroldis Chapman has not worked out as they would have hoped. Even though he’s struck out 24 batters in 13 innings, he’s also allowed two home runs and seven earned runs. He’s also walked 17 batters, so even though he’s only given up nine hits, he has a WHIP of 1.90. Chapman was expected to be a massive part of this pen and the go-to high-leverage left-hander.

The Pirates’ two-time All-Star closing pitcher, David Bednar, also hasn’t been anything like himself this year. He’s already given up as many earned runs this year as he did last year, in 2022 and 2021. He only needed 15 innings to allow 15 ER. He’s also already allowed three home runs. Bednar is below the 15th percentile of exit velocity and barrel rate after ranking in the 72nd percentile and 87th percentile of each stat.

That’s five pitchers the Pirates were going to be heavily relying on in 2024 either injured or performing well below expectations, two of which were their go-to left-handed relievers.

Sure, you can lose one, maybe two guys, but five pitchers is almost a full bullpen. Right now, the only thing they can do is maybe promote Mlodzinski. There isn’t any readily available solution unless they plan on trading for bullpen help, which might be a possibility, but I do not see that happening in May.