With the implementation of the opener in Major League Baseball also came the introduction of the primary pitcher. That was Yarbrough's primary role in 2018. He totaled 147.1 innings despite making just six starts in 38 appearances, and the results were relatively strong despite underwhelming peripherals. He didn't even crack 90 mph on average with his fastball, but his slider and cutter were effective enough against left-handed batters. It was a different story against right-handed hitters -- 10.1 K-BB%, .324 wOBA, 4.34 FIP. Further, Yarbrough's ERA jumped from 2.63 the first time through to 4.29 the second time through (as a reliever), which suggests that both Yarbrough and the team may be better off shortening him up. Factor in the caliber of the offenses in his own division and Yarbrough looks like a low-upside pitcher with the downside of a true middle reliever, so waiver-wire fodder in mixed leagues.

Yarbrough spent the majority of 2015 with High-A Bakersfield in the California League, where he finished with a 4-7 record and 3.76 ERA in 16 starts. He posted a 4.11 strikeout-to-walk ratio, .266 batting average against, and 1.28 WHIP. Part of his high batting average against can likely be explained by his .324 BABIP, which was much higher than the .266 BABIP he finished with in 2014. Yarbrough had a groin injury in June that sent him to the 7-day DL, but should be healthy to start 2016. Yarbrough's arsenal of pitches includes an average fastball and curveball to go along with an excellent change-up. He moved up from number 11 to number eight on the Mariners prospect rankings during 2015 and is estimated to make the MLB during 2016. Scouts believe has back-of-the-rotation potential, but will most likely end up in the bullpen long-term. If Yarbrough pitches well to start 2016, there is a good chance he could be called-up to the MLB at some point as a lefty reliever.