Gustave, 22, could turn out to be one of the more interesting stories in Royals camp. As a Rule 5 player, he must stay on the Royals' 25-man roster all season or be offered back to the Astros.
Gustave's intriguing tools -- he can reach 101 mph, but normally throws around 96-97 -- is one of the reasons the Royals are considering an eight-man bullpen. They would need to protect Gustave, who has never pitched above Class A.
"He's got a lot of talent," said Rene Francisco, Royals vice president/assistant general manager for Major League and international operations. "A great arm, very lively arm. Like a lot of young guys, he can struggle with command. But he's just a kid. A lot of room there for improvement."
The Royals took Gustave in the Rule 5 Draft largely on Francisco's recommendation. Francisco managed him for a team in the Dominican Republic last fall.
"We put him in a lot of high-leverage situations and he responded very well," Francisco said. "It's going to be interesting to see what we have with him."
Gustave threw his first bullpen session, about 30 pitches worth, on Saturday. While his velocity was impressive, his command was noticeably off.
"Just nerves, probably," Royals vice president/assistant general manager J.J. Picollo said. "A lot of guys come out early in spring and really try to impress everyone. You tend to do that unless you know you've made the team."
There are, of course, no guarantees for Gustave, who has averaged 6.7 walks per nine innings during his Minor League career. Last season, however, at Class A Quad Cities of the Midwest League, he cut that ratio down to 3.3.
Manager Ned Yost got his first look at Gustave in action on Saturday.
"It's just a side session, but I liked what I saw," he said. "The ball really explodes out of his hand. He's got a quick arm.
"I want to see him a few more times before I say much else."