The 22-year-old Samuel's powerful fastball and nasty slider have scouts talking. But so do his 41 walks in 42 2/3 innings and his 6.12 ERA.
The righty has been dealing with control problems all season, and was recently removed as the closer at Double-A Springfield after giving up three earned runs in back-to-back appearances on July 24 and July 26. Those struggles have opened a door for fellow reliever Eduardo Sanchez, 20, who may soon pass Samuel on prospect lists.
"Hopefully this is a little bit of a wakeup call for [Samuel]," said Springfield manager Pop Warner. "You have to be consistent in this game.
"It hasn't been for lack of stuff. He has big league stuff. He just has to be able to harness it and be able to command the strike zone."
Samuel struck out 85 batters and allowed just 39 hits in 54 appearances for Class A Palm Beach last year. But he walked three and gave up three earned runs in his first appearance of the year for Springfield on April 11 and has struggled since. Samuel walked at least one batter in 18 of his first 22 appearances and until last week, had more walks than innings pitched on the season.
"There's no doubt that you worry." said Cardinals general manager John Mozeliak. "Because you have to get that under control so that you can be more effective. But when I look at him and where he was a year ago, he's making the right strides.
"The big thing is just trying to get him to become more consistent. When you're getting the pressure of trying to finish a game and you're having trouble with your command, it just makes sense to try and elevate something. You want him to be working in high-leverage situations, and some of that can still be used in the seventh or eighth."
Samuel, who had 22 saves in 26 chances before losing his spot to Sanchez, seemed to find something in June when he walked only four batters in 11 innings and had a 3.27 ERA. But despite more struggles in July, the confident Samuel wasn't happy with the move.
"He didn't like it," Warner said. "He didn't like it at all. We talked to him and said, 'Hey, at the end of the day, you have to pitch better. You have to throw strikes. You can't walk guys, especially if you are going to be out there closing games. You can't go out there and walk three guys an inning. You're asking for disaster.'"
Samuel has worked with pitching coach Bryan Eversgerd during a few bullpen sessions in between outings and had back-to-back scoreless -- and walkless -- outings on Aug. 5 and 6. It's early, but Samuel hopes that things may be turning around.
"It's been a little rough, but I'm still battling," Samuel said through interpreter and Springfield catcher Tony Cruz. "I had a few outings that were bad but I'm feeling better.
"My mechanics changed a little bit and that's why I was walking more people. But I feel better now."
The presence of Sanchez made the decision to switch things up easier for the Cardinals' front office. Sanchez burst onto the scene with his high-90s fastball and impressive breaking ball this year at Palm Beach. He had a 1.44 ERA and 26 strikeouts to just five walks in 19 appearances before being promoted to Springfield.
His success continued there, where he has a 2.43 ERA in 37 innings and has 44 strikeouts against 13 walks. He's also shown an ability to get out of a jam. Sanchez put runners at first and third with one out in the ninth against Tulsa on Friday with Springfield leading, 4-3. But with the tying run 90 feet away, the 20-year-old struck out the next two hitters to close it out.
The last hitter didn't have a chance, going down swinging on three pitches -- a 98-mph fastball, an 82-mph breaking ball, and another 99-mph heater.
"That kid's something special, I'll tell you," Warner said after the game. "He has a lot of upside. ... He doesn't scare. That's one thing that we really notice about him. He doesn't get intimidated. He goes out there and he's in control of the situation."
Mozeliak moved from a press-level suite to an open seat behind home plate when Sanchez trotted in from the bullpen for the ninth.
"You hear about movement, you hear about the breaking ball. I just wanted to see it for myself again," Mozeliak said. "He's got a live arm. Nothing comes out of his hand straight. You saw the flashes. It's exciting, especially at his age. He's been throwing very well and obviously having both guys on the club gives you a lot of flexibility."
And while Sanchez appears unfazed by the added significance of the ninth -- he said through a translator that he "never" feels pressure on the mound -- the Cardinals must now find a way to turn things around for Samuel.
"There is not as much on the line now so he can get his mechanics to where he doesn't have to worry about going out there every single time and getting three outs and if he doesn't, we lose," Warner said. "And it's happened. The last couple of times out, he's been pretty good. It's not to say he's not going to be back as closer again, but we're trying to get him back to where he should be and then we will take it from there.
"They are both little fireballers, and if they can command the strike zone like they should, they will help us out in St. Louis."
B.J. Rains is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.