LOWELL, Mass. — The relief pitcher walked in from the outfield during batting practice.

Manager Bruce Crabbe waved him over.

“From now on,” Crabbe said in a soft but undeniably firm voice, “you run in. You don’t walk.”

Another group of players did run in, to the dugout. But they were being too casual about reporting to the batting cage.

“Let’s go,” said hitting coach George Lombard, making a circular motion with his hands.

Life with the Lowell Spinners is all about learning to be a professional baseball player.

“They’re just pups,” said Lombard, 34, who spent time with the Sea Dogs (2004), part of his 16-year playing career.

“Some of them don’t know how to carry themselves. They’ve got to learn it’s a job. They’re not in college. They’re doing this for a living. It’s a grind.”

And it seems like such a long way to the major leagues.

The Lowell Spinners are a short-season Class A team that begins play in June. There are two more levels of Class A leagues before a player can reach Double-A (the Sea Dogs), and then Triple-A (Pawtucket), and then, of course, the bigs.

It’s a long way to the majors, but players do make it. When former Spinners and Sea Dogs pitcher Felix Doubront pitched for Boston last year, he became the 41st Lowell player to reach the big leagues.

And jumps can be made quickly. Two of the Sea Dogs starting pitchers this season, Alex Wilson and Jeremy Kehrt, pitched for the Spinners last year.

After Jacoby Ellsbury was drafted in 2005, he played for Lowell that year. At the end of 2006, Ellsbury was celebrating an Eastern League championship with Portland, and in 2007 he was stroking four doubles in the World Series.

The Spinners’ roster is filled with recently drafted players from college, high school players who were in the Gulf Coast League in Florida last year (the lowest level of the minors in the U.S.), and international players who may have been pros since they were 16.

“All these guys are going to have their growing pains,” Crabbe said. “It’s patience, for sure, that needs to be practiced.”

Still, Lowell has some of Boston’s most intriguing prospects, including the first two draft picks from this month, infielder Kolbrin Vitek and outfielder Bryce Brentz.

Here’s a look at six players who could be in Portland in the coming years, some as soon as next summer.

  • Vitek, 21, was drafted 20th overall from Ball State and was given a bonus close to $1.4 million. He batted .361 this season at Ball State, with 17 home runs. At 6-foot-3, 195 pounds, he’s expected to be able to hit for power.

Vitek has already moved from second base to third — maybe because he has that power potential and because Boston has a second baseman (Dustin Pedroia) signed through 2015.

In his first seven games for Lowell, Vitek was batting .333 (8 for 24).

“He has plate discipline and there is life in his bat,” Crabbe said. “He’s athletic. I like the way he handles himself.

“Who knows if he’ll have success right away, but you see the potential.”

  • Brentz, 21, had a monster sophomore year at Middle Tennessee State, batting .465 with 28 home runs. An ankle sprain slowed him this season (.348, 15 homers), which is why Boston could get him with the 36th overall pick ($900,000 signing bonus).

“You watch him take batting practice and he’s hitting balls in the trees out there,” Crabbe said, pointing beyond the wall in left-center.

“He has bat speed, plus a cannon of an arm.”

Brentz, 6-foot, 195 pounds, was cranking balls out during batting practice Tuesday. And he poked an opposite-field double over the right fielder’s head that night. So far, Brentz is batting only .130 (3 for 23).

  • David Renfroe, 19, is also off to a slow start (2 for 23), but Boston is banking on his skills as an infielder and solid hitter.

Like some other Red Sox prospects, Renfroe was a star high school player with a college scholarship in hand, so it took a big bonus for him to turn down the scholarship (which is why a player like Lars Anderson fell to the 18th round and then signed for $800,000).

Renfroe was picked in the third round last year and was given $1.4 million. He signed late and did not play in 2009. He also is playing third base (when Vitek is the designated hitter).

“He’s a little overmatched right now,” Crabbe said. “Defensively, he’s secure. But like I said, there will be growing pains for a lot of them.”

  • Brandon Jacobs, 19, is 5-11 and 240 pounds. He was going to be a running back for Auburn until Boston drafted him in the 10th round last year and signed him for $750,000. He’s an outfielder who can crush the ball.

“Very raw. Athletic. Just has to learn to do it every day,” Lombard said.

He’s batting .333 (8 for 24) with three doubles and four RBI.

  • Madison Younginer, 19, was considered “one of the best raw arms in the (2009) draft” according to Baseball America. He dropped to the seventh round, where Boston took him and gave him close to first-round money ($975,000).

He has a 95 mph fastball, a hard curve and a developing change-up.

In his pro debut last week, Younginer pitched five scoreless innings, allowing one hit and one walk while striking out three.

“He worked efficiently and effectively and was able to command the fastball, getting it to the lower half of the zone,” Lowell pitching coach Laz Gutierrez said. “That was pretty impressive for a kid of that age.”

But inconsistency is the norm at this level. Younginer struggled in his last start on Thursday, allowing six hits and six earned runs.

  • Roman Mendez, 19, signed with Boston three years ago as a free agent from the Dominican. He throws a fastball and a slider, with emphasis on the P-word (potential).

Mendez recorded a 1.99 ERA in the Gulf Coast League last year. In his last start for Lowell, his allowed two hits and one run over five innings.

There are other potentially strong players in Lowell, including starters Tyler Wilson (plus sinker) and Hunter Cervenka (power left-hander), and center fielder Felix Sanchez (Ellsbury-plus speed).

If their potential pans out, these players will climb the minor league rungs, eventually landing in Hadlock Field, with their sights on Fenway. 

Staff Writer Kevin Thomas can be contacted at 791-6411 or at:

kthomas@pressherald.com