Why the D-Backs have used experienced arms to fill fifth rotation spot

All season, the Diamondbacks have opted for pitchers with major league experience to fill their fifth spot in the rotation. First, it was Caleb Smith. Then Humberto Castellanos got the call. Tyler Gilbert has started three times. And now, Luke Weaver — who started the season as a long reliever before going on the 60-day IL with an elbow injury — is settling into the role.

On Tuesday, pitching coach Brent Strom announced that Weaver will be the club’s starter Saturday night against Minnesota. Given that Weaver appeared for three innings out of the bullpen with Kyle Nelson serving as an opener on Sunday, the decision doesn’t come as a surprise.

But it does continue the trend of relying on experienced arms, even as a number of prospects knock on the door.

Although the Diamondbacks’ system doesn’t have any standout pitching prospects like it does on the offensive side, it is deep with intriguing arms. Tommy Henry, Ryne Nelson, Drey Jameson and Brandon Pfaadt — the first three of whom are already in Triple-A — are considered to be the closest to the majors.

Jameson is tantalizing with his velocity, topping out in triple digits, but the Diamondbacks want him to tame his velocity and focus on landing pitches — especially his off-speed offerings. Pfaadt, meanwhile, needs to continue learning how to attack batters, according to pitching coordinator Dan Carlson.

But Henry and Nelson are “major league ready,” according to Carlson, even if both are working on their control in Triple-A Reno.

“They need to have better quality misses in good areas and they really, really have improved,” Carlson said. “Probably over the last three weeks, they've really gotten really, really sharp. They look fantastic.”

In his last three starts, Henry has struck out 22 and walked just two. Over that same span, Nelson has struck out 24 and walked six.

Nelson’s improvement has been especially notable after he started the season with his velocity down into the low-90s. After a mechanical adjustment in Reno, he’s back up into the mid-90s and topping out at 98.

Even with that growth, though, it’s Weaver who will continue filling out the Diamondbacks’ rotation.

“There's a little bit of a pecking order,” Carlson said. “And with the front office, they know exactly what they're doing, when they want it to happen.”

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Part of the calculus, too, is that Weaver impressed on Sunday, striking out four in three innings of one-run ball.

“I liked the fact that I saw 94 (mph),” pitching coach Brent Strom said. “I didn't see variation in velocities. I didn't see the 95 then the 91 or the 90. I saw a consistent velocity. I saw some really good change-ups. Breaking ball's still a work in progress and he threw a couple that were pretty good.”

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Dallas Keuchel returns with mixed results

Former Cy Young winner Dallas Keuchel appeared in the Arizona Complex League for the first time on Monday after signing a minor league contract with the Diamondbacks last week.

According to Strom — who worked with Keuchel in Houston for five years at his peak — Keuchel threw approximately 80 pitches and did “fairly well.”

“I saw a lot of strikes,” Strom said, listing off the positives from Keuchel’s outing. “His sinker was very good, according to the Trackman data that we got.”

The flip side is that Keuchel’s fastball wasn’t where Strom wanted.

“I still think we have some work to do in terms of getting the arm strength and the fastball back to where I was hoping it would be,” Strom said. “… I need to get back with him is elevating the fastball.”

Strom is planning on going to Salt River Fields on Thursday’s off-day to watch Keuchel’s throwing session.

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Theo Mackie covers Arizona high school sports, the Arizona Diamondbacks and Phoenix Rising FC. He can be reached by email at theo.mackie@gannett.com and on Twitter @theo_mackie.

This article originally appeared on Arizona Republic: Diamondbacks continue to use experienced arms to fill out rotation