Boston has a bunch of starting pitching options in front of them right now, and to this point, most of them have average-or-better hurlers with a history of success. Some have injury issues, some had their best years at the right time, but generally speaking, they're all expected to produce at relatively similar levels.
Francisco Liriano, though, whom Sean McAdam is reporting Boston is looking at, is a different type of starting pitcher. Liriano is a former all-star who has had some monster seasons in the past, but generally, he's very hard to predict, and has been a below-average pitcher when you sum his career up. There were issues in 2012, especially, as he bounced between the rotation and the bullpen, and ended up leaving the Twins for the White Sox, only to disappoint some more with very similar stats.
Because of this, Liriano as a depth option, someone to shove in the bullpen or attempt to sign to a minor-league deal, makes a lot of sense. The latter is essentially not going to happen, for a 29-year-old who posted a 112 ERA+ as recently as 2010, but then again, maybe it could. After all, Liriano has a history of injury issues, and owns a 79 ERA+ over the last two years. To really hammer that home for you, Aaron Cook produced a 77 ERA+ for Boston this past season, and every other starter with at least 50 innings for the Red Sox bested that mark. There's a non-zero chance that the league collectively has had enough of guaranteeing Liriano a roster spot and contract, and it turns into a battle of who can put the shiniest opt-out or incentives into a non-guaranteed deal.
Bullpen or minor-league deal: that's about the only way to feel comfortable about Liriano. He hasn't been terrible because of luck, or because he's pitching while hurt, or anything like that. Liriano's issue is that he has one pitch worth its weight in stitching, his slider. It's a fantastic pitch when it's on, and it's the reason Liriano has had as many great moments as he has in his career.
The issue, as you might have already surmised given how poor he's been of late, is that the slider isn't always there. The slider has been there in all of his best seasons, and it's not when he's awful. The result? Three full campaigns out of six with an above-average ERA, and three with well below-average, five-plus ERA seasons.
Sticking him in the pen could allow you to see if the slider is working. Putting him in the minors, or inviting him to spring training, allows for the same. Guaranteeing him much of anything is asking for trouble if it's going to be the third-straight year he can't pull himself together for more than a few innings at a time.
This is very likely a case of Boston just keeping their options open and monitoring the market. If other clubs are interested in giving Liriano a shot, he becomes less intriguing, as that means he'll require resources to acquire. If not, though, and Boston can work something out that doesn't cost them much in the way of guaranteed resources or a roster spot, and he becomes appealing for a trial run.