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6/25/2014 10:00 A.M. ET

Pipeline Perspectives: Astros have Minors' top rotation

Lancaster loaded with starting pitching talent despite Appel's struggles

There's a good amount of subjectivity regarding baseball prospects. With the evaluation of talent being in the eye of the beholder, finding consensus is often difficult. Even Jim Callis and Jonathan Mayo of MLBPipeline.com don't always see eye to eye. They discuss their viewpoints regularly in a feature called Pipeline Perspectives. Submit a topic for them to debate.

As strange as it may sound, the headliners in the best rotation in the Minor League consist of a guy with a 10.48 ERA, two currently on the disabled list and a former 19th-round pick. Yet all four of them have the potential to become front-line starters.

The Astros entered the season with the best farm system in baseball, so it's no shock that they'd be able to put together a quality Minor League rotation. They did just that at high Class A Lancaster, where they've used a tandem starter system for much of the season.

So far, JetHawks pitchers have combined for a 3.93 ERA -- an impressive mark considering that Lancaster might be the most difficult place to pitch in the Minors because the wind always seems to howl out toward the fences at The Hangar, and the California League favors hitters as a whole. That ERA is the franchise's lowest since 2000, when it was a Diamondbacks affiliate. Not coincidentally, Lancaster won the first-half title in the Cal League's Southern Division and is tied for the circuit's best record at 46-30.

The No. 1 overall pick in the 2013 First-Year Player Draft was supposed to be the centerpiece of the JetHawks' staff, but right-hander Mark Appel has been anything but that. He got battered in his first four starts, which the Astros attributed to a January appendectomy and difficulties adjusting to the tandem system. Sent to extended spring camp for a month, Appel gave up 10 runs on 10 hits in 1 1/3 innings in his first start back at Lancaster.

Appel is still looking for his first victory and his first quality start after seven outings, and his ERA is a grisly 10.48. The good news is that he's showing the same stuff that got him drafted No. 1 a year ago. But Appel is not locating it well enough down in the strike zone. He averaged 94 mph and reached 97 with his fastball on Sunday, and he has shown flashes of a plus slider and solid changeup.

While Appel has struggled terribly, a left-hander drafted 18 rounds later than he was has dominated. Signed for $40,000 out of a Baltimore high school by the Orioles in 2012, Josh Hader came to Houston last July in a trade for Bud Norris. Hader currently leads the Cal League in ERA (2.27) and opponent batting average (.188), and he has struck out 78 in 71 1/3 innings.

After throwing in the mid-80s for most of his high school senior season, Hader has gotten stronger and now operates in the low 90s and can hit 96 mph with his fastball. He has made significant strides with his changeup this season, though his slider remains inconsistent. Hader's lanky build and his low-three-quarters arm slot have earned him some Chris Sale comparisons.

The other two potential front-line starters at Lancaster are sidelined at the moment, though that doesn't diminish their upside. Lance McCullers Jr., who hasn't pitched since June 8 because of a sore back, likely will return before fellow right-hander Vincent Velasquez, who has been out since May 9 with a groin injury.

A supplemental first-round pick in 2012, McCullers might have the most overpowering stuff on the staff. Both his 93- to 98-mph fastball and his hard curveball have the potential to become well-above-average offerings. McCullers' power is more notable than his polish, as evidenced by his 66/30 strikeouts-to-walks ratio and his 4.58 ERA in 57 innings.

Velasquez was a second-rounder and had a strong pro debut in 2010, but Tommy John elbow surgery that winter sidetracked his career for a while. He has performed well since reaching full-season ball in 2013 and got off to a fast start this season, going 4-1 with a 2.89 ERA and 33 strikeouts in 28 innings before getting hurt. Velasquez's 92- to 94-mph fastball and changeup project to be plus pitches, and he's been making progress with his curveball.

There's a sleeper in the Lancaster rotation, too. Chris Devenski waited 25 rounds in the 2011 Draft before the White Sox took him, and he came to the Astros the following summer as the player to be named in a trade for Brett Myers. Thanks to a 90- to 94-mph fastball and an effective changeup, Devenski has a sparkling 68/11 K/BB ratio in 66 2/3 innings this year.

The Reds' Double-A Pensacola rotation was Jonathan Mayo's choice as the best in the Minors, and the Blue Wahoos' starters are having better present years than those of the JetHawks. But no rotation has a brighter future than Lancaster's, a major reason that better days are ahead for Houston.