Chicago Cubs claim left-hander Randy Rosario off waivers from Twins

The Chicago Cubs made an addition to their bullpen on Friday, claiming left-handed reliever Randy Rosario off waivers from the Minnesota Twins.

During the 2017 postseason, the Chicago Cubs bullpen was a glaring weakness, whether the team ultimately won or lost. Friday, the team made its first of many potential moves to upgrade the relief corps for 2018 and beyond.

The Cubs claimed left-handed reliever Randy Rosario off waivers from the Minnesota Twins. With the move, their 40 man roster now stands at 33 players.

Dominant minor league career

While Rosario has just 2 1/3 innings of MLB experience, he also is just 23 years old. Since signing with the Twins in 2010, Rosario has been successful at every minor league level. In 107 games (55 starts), Rosario is 18-22 with a 3.37 ERA.

Though he has experience as a minor league starting pitcher, Rosario became a full-time reliever in 2017. Between Advanced-A Fort Myers and Double-A Chattanooga, Rosario had a 3.84 ERA (34 games, 61 innings pitched).

In addition to a solid ERA, Rosario posted an eye-popping .169 batting average against lefties in 17 innings. For the sake of comparison, righties hit .296 against him in 40 1/3 innings. He has all the makings of a future left-handed specialist.

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Uncertainty in 2018 bullpen

While Rosario faced righties more frequently, the fact of the matter is that he dominated lefties last season. Between the Washington Nationals and the Los Angeles Dodgers, the Cubs faced two teams in the postseason with tremendous left-handed hitters.

On the one hand, Brian Duensing was dominant both in the regular season (2.74 ERA, 62 1/3 innings) and the postseason (1.69, 5 1/3 innings). On the other hand, Mike Montgomery (2.49 ERA, 61 1/3 innings) was successful as a reliever in the regular season but not in the postseason (16.62 ERA, 5 1/3 innings).

Duensing is a free agent and it is not clear if the Cubs will retain him for 2018. Really, the team would be foolish not to re-sign him; he signed a cheap contract and turned out to be reliable all season long.

Montgomery will be back with the Cubs in 2018, albeit with an undetermined role. The Cubs could move him to the starting rotation full-time, or he could continue his role as a sixth starter/long-reliever.

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Ultimately, there is no such thing as having too much pitching depth. At 23 years old, Rosario could contribute at some point in 2018, even with Duensing and Montgomery on the roster. All in all, acquiring him is a low-risk, high-reward move for the Cubs in 2018 and possibly beyond.