Amid a flurry of trade talk and free agent speculation, the Boston Red Sox and Seattle Mariners have pulled off a trade in which Boston trades starting pitcher Wade Miley and reliever Jonathan Aro to Seattle in exchange for relief pitcher Carson Smith and starter Roenis Elias.

The two primary pieces in this exchange are Miley and Smith. And it's not everyday that the team getting the relief pitcher ends up getting the better end of the deal, but that is what you have here.

In Miley, the Mariners get a 28-year-old pitcher who went 11-11 last season with a 4.46 ERA, a 3.81 FIP, and a bWAR of 2.5. Miley piled up 193 2/3 innings and struck out 6.8 batters per nine while walking 3.0, posting a 1.368 WHIP while allowing 17 home runs last season. He has a lifetime ERA of 3.95 and 3.80 FIP, with his best season coming in 2012, his rookie campaign, when he went 16-11 with a 3.33 ERA in 194 2/3 innings, making the All Star team and finishing second in the Rookie of the Year balloting.

But in 2015, his 4.46 ERA was the highest of his career since becoming a full-time big league starter. He doesn't strike guys out and instead relies on ground balls to get his outs. He had a ground ball percentage of 52.0% in 2013 and 51.1% in 2014, but it dropped to 48.8% in 2015. 

He is a back-end starter, which isn't a bad thing, and can occasionally dazzle.

In return, the Red Sox get a 25-year-old reliever who appeared in 70 games for Seattle last season and put up a 2.31 ERA and a FIP of 2.12. His bWAR of 2.3 is just two-tenths of a win above replacement less than Miley, and he did that in just 70 innings, compared to Miley's 193 2/3. 

Carson struck out 11.8 batters per nine innings last season and walked just 2.8, with a WHIP of 1.014 and an opponents' batting average of just .192. 

His most devastating pitch is his slider, which he threw 45.0% of the time. The only pitch he threw more was his fastball, 48.7% of the time. He dabbles with a change-up, but is mainly a two-pitch pitcher. And, wouldn't you be with a slider like this?

In other words, Boston just turned a number-four or number-five starter into a top-shelf middle or late-inning relief pitcher. Not a bad day's work for team president Dave Dombrowski. 

Of course, one note of caution on Carson. He seemed to lose some steam in the second half of the season. Compare his first half and second half numbers.

Those second half numbers are still pretty good, but the drop could be a result of one of two things, either the young pitcher fatigued or the league started to figure him out a bit.

Seattle already has a strong top-of-the-rotation with Felix Hernandez, and Taijuan Walker in the numbers-one and two slots. Recently-acquired Nate Karns will battle with Miley for the number-three spot. 

At the end of the day, the Red Sox did well to find a solid young bullpen arm for the cost of a back-end rotation starter, one they didn't need anyway.