We were treated to one of the best bullpens in franchise history last season. Possibly even the best. When Walt kept the band together, it was easy to assume we were in for another season of shut-down relief.
So far this season, the bullpen has been mediocre-to-fair - depending on where you look. They have collective ERA (3.76) and OPS-against (.700) sitting just about NL average. Adjusting ERA for park, they're still pretty middling - 8th in the NL, 12th in majors. Most of the leverage or win probability indicators - including WPA - also puts them about middle of the pack.
To go with a excellent rotation, you'll gladly take a league-average bullpen. But the talent level in the Reds' bullpen is better than league average.
Specifically, the Reds have three closer-caliber arms at the back of the bullpen, who are being paid accordingly. Chapman, Broxton and Marshall make a total of $12M this season - with contracts that increase from here. One the one hand, the Reds are getting three great relievers from the price of CoCo Cordero. On the other hand, Cordero's CoContract is a terrible point of comparison.
The Reds are no longer closer poor and these guys aren't breaking the bank. But we're obviously expecting a little bit more over the remaining large amount of games of the season.
I don't really think Sean Marshall is part of the problem here. He's allowed some inherited runners to score lately, but his 50% strand rate isn't sustainable (it's been 73% over his career). His adjusted ERA puts him at third-best on Reds' staff, ignoring innings, and his K-rate and BB-rate both look good (8.5-per-nine and 2.8-per-nine respectively).
It's true he hasn't looked great lately trying to clean up other relievers' messes, but has only been pinned with one "melt down" this season (ie, "when a reliever's WPA is less than or equal to -0.06 in any individual game").
His relatively unblemished record benefits from being injured and under-used. It's not clear if Baker has been purposefully coddling him a little since he returned from the DL, but Marshall has been kicked to the margins. He's the highest paid and, arguably, second most-talented reliever in the bullpen. But he's being used as a 1-2 batter situational lefty.
Since returning from the DL on April 27, Marshall has averaged less than 2/3 IP per appearance, averaged less than 2.5 batters faced and thrown just 9.4 pitches per appearance.
After he gave up his first earned run back on May 8th, he's pitched just a total of 1.0 inning and thrown 22 pitches in 11 days. Maybe there's a lingering issue with his stamina, but by all accounts it looks like he's been converted into the best paid LOOGy in the league. You'd forgive him for forgetting how to throw a curveball.
I've already commented on this in the threads, but here's what I think is wrong with Chapman. It's not his fastball velocity, which has averaged 97.2 mph so far - consistent with where he was in May last season. It's not his fastball reliance - he's throwing at the same 85%/15% fastball/slider split he has over his career. It's not his slider - which again ranks among the league's best by FanGraphs pitch value (adjusted for 100 pitches).
It's his fastball. He doesn't seem to know where it's going and it doesn't seem to have much of any movement when it goes. Hitters are catching up and fouling it off more. It's possible they're sitting on it more than they did last season - he throws it A LOT - but when it's on, sitting on it still doesn't do you much good.
Getting the fastball back will be some kind of alchemy of confidence restoration and chat with Bryan Price. I think it'll be back soon, like it has been before.
Broxton was able to make it as a post-power reliever last season. This year, his cutter has let him down. He's already allowed 2 HRs on that pitch, after not allowing any last season. Broxton's record is still marred by his disasterous appearance following an unexplained 6-day lay-off, but if he can't get that pitch back, there could be more rough days ahead.