In the 112-year history of the American League, only six 24-year-old rookie left-handed relievers threw at least 74 innings in a season. Five of them pitched in the 1980s; the sixth pitched in 2013.
T.J. McFarland, formerly a starter in the Cleveland minor league system, came to the O’s in December 2012 as part of the Rule 5 draft. Since he made the O's out of Spring Training, he had to stay on the 25-man roster all year or hit the waiver wire. He stayed and threw 74.2 innings, all in relief except for a dismal short start in June. That's not a lot of playing time for anyone, let alone a rookie, so take his opponents' batting line of .277/.337/.400 with a grain of salt. That's slightly worse than the average AL mark of .256/.320/.404, but we need to see more from him to truly gauge his talent level.
There’s a lot to like about McFarland. To start with, he walked batters at a below-average clip (8.5%) and got ground balls way more often (58%) than than the average AL reliever. 58% is Jim Johnson territory, so it’s no surprise that McFarland also relies on his sinker to get outs. The sinker is one reason why he didn’t give up a lot of hard contact. His opponents' line-drive rate of 18% was fourth-best among all AL relievers this year. That’s something to be proud of. The low line-drive rate also highlights his relatively high BABIP of .319. If you give up line drives that infrequently but many balls still fall in for hits, you're getting unlucky.
Another aspect worth noting is that McFarland didn't show significant platoon splits: .330/.315 wOBA against lefties/righties. We'd expect this kind of performance given his experience as a starter, but it's nice to see some proof in the majors. The lack of splits supports Showalter's use of McFarland as a long reliever and spot starter instead of just a LOOGY. In 2013, only one AL reliever had more appearances of 2+ innings than McFarland did.
Two-and-a-half negatives stuck out. One, McFarland had a poor strikeout rate -- just 17.5%, compared to the average AL reliever's K rate of 22%. That rate puts him in the bottom tier of pitchers. Two, his HR/FB was high - over 12%, although this was true of nearly all the O’s pitchers this year, especially at OPACY. And the relatively small number of fly balls meant his ERA wasn't a disaster. The half-negative is his walk rate. It’s below-average, yes, but relievers really shouldn’t be walking batters that often unless they are striking out a lot, also.
So it seems McFarland is building a reputation as a pitch-to-contact ground ball specialist. Careers can be made this way, and given that McFarland will play his age-25 season next year, he certainly can make one for himself. In 2014 I'd expect slightly fewer runs to cross the plate while he's on the mound, based on the likelihood of his BABIP regressing to the mean. Since he's 3/4 reliever and 1/4 starter, I'm not quite sure what his BABIP target is, but it's lower than .319 (assuming he's a major-league caliber pitcher, that is).
Given the poor quality of the O's starting rotation, having a lefty long reliever with minimal platoon splits is nice. And if McFarland can either increase his strikeout rate or decrease his walk rate, he'll find more and more people talking about him as a starter instead.