Farrell, whose father manages the Boston Red Sox, made his big league debut with the Royals in 2017 but has bounced from Kansas City to the Dodgers to the Reds to the Cubs in minor trades and waiver claims over the past several months. His lone outing in Kansas City produced nightmarish results (five runs on seven hits and three walks in 2 2/3 innings), but he enjoyed better success in a larger sample with Cincinnati. In 10 1/3 innings as a Red, he allowed three runs on just five hits, though he also walked seven in that time. Overall, Farrell’s first taste of the big leagues resulted in a 5.54 ERA and a 9-to-10 K/BB ratio in 13 innings.
Farrell has, however, produced solid Triple-A results in 2016-17, working to a combined 3.83 ERA with 8.5 K/9, 3.5 BB/9 and roughly a 36 percent ground-ball rate in 199 2/3 innings. He has a pair of minor league options remaining beyond this season, so if the Cubs choose to keep him on the roster this winter, they could option him to Triple-A Iowa next spring without first exposing him to waivers. Alternatively, the Cubs could try to pass Farrell through waivers themselves in hopes of retaining his arm as a depth piece without the need of committing a 40-man roster spot.
The 27-year-old Pena, meanwhile, averaged 93.4 mph on his heater in 34 1/3 innings with the Cubs this year. He also averaged a hearty 9.7 K/9 against a more troublesome 4.7 BB/9 and a sub-par 34.7 percent ground-ball rate en route to a 5.24 earned run average.