Callups can infuse spark into fantasy lineups

May is an exciting month in fantasy baseball. As owners grow impatient of slow starters, a new batch of potential contributors starts to arrive in the form of Minor League callups. Rookies cannot be lumped into one group. Each player's fate will be decided based on his skill level, readiness, opportunity and role. Fantasy owners who make smart additions in May could ride five months of production from key youngsters into a championship run. But those who waste valuable free-agent resources on the wrong prospects will end up with massive lineup holes during the summer. Here's a look at the potential fantasy value of some new callups and upcoming additions:

C.J. Cron (6) -- It took Cron just 28 Triple-A games to rack up six homers, 26 RBIs and a .319 batting average. The stellar numbers, combined with injuries to Josh Hamilton and Kole Calhoun, have earned Cron his first taste of big league action. The 24-year-old had a monster season in 2012, when he collected 27 homers and 123 RBIs in 129 games, but he was merely good in 2013. Cron is ranked as the Angels' third-best prospect by MLB.com, and he deserves a bench spot in 12-team leagues. Those in deep formats should feel comfortable giving Cron a one-week audition in the starting lineup. He went 5-for-12 (.417) in his first two Major League games, so he should draw more starts in the coming days.

Marcus Stroman (13.09) -- With a rotation spot on the line, Stroman struggled in Spring Training with the Blue Jays. He posted a 13.09 ERA, giving up 21 hits in 11 innings. The 23-year-old's poor spring numbers were not the result of one bad outing, as he didn't have a single dominant performance in six tries. As a result, Stroman opened 2013 in Triple-A, where he dominated batters to the tune of 36 K's and a 1.69 ERA in 26 2/3 innings. The Stroman hype train is moving at full speed right now, and he will likely get a rotation spot at some point in May. But fantasy owners should consider pumping the brakes a bit, as the right-hander could have some rocky times in his first regular-season exposure. The American League East is home to many hitter-friendly parks and powerful, veteran offenses. If Stroman struggles with his control, teams such as Baltimore, Boston and New York know how to make him pay on the scoreboard.

Trevor Bauer (1.10) -- While Stroman may need some adjustment time at the Major League level, Bauer has already been through those struggles, and his time to break out could be coming soon. The right-hander is dominating Triple-A this season to the tune of a 1.10 ERA, a 1.01 WHIP and a 31-to-9 strikeout-to-walk ratio in 32 2/3 innings. Bauer was inconsistent last year, and he could not maintain a quality ERA in the Minors or the Majors. This time around, he is showing better control, and he is working deeper into games. Bauer was impressive during a six-inning spot start with the Tribe earlier this season, and even though the team added Josh Tomlin to the rotation this week, it is clear that Bauer's time is coming soon, and he may be the better option to help fantasy owners this season.

James Jones (5) -- The early-season struggles of Abraham Almonte have opened the door for Jones to get his first crack at the Majors. The 25-year-old possesses plus speed, as he stole five bases in 20 Triple-A games this season, after swiping 28 in the Minors a year ago. Speedsters often have an immediate impact on fantasy rosters -- they only need to reach first base to show off their greatest skill -- but Jones should stay on waivers in most mixed leagues for now. The Mariners do not have stars in the outfield, but they have a deep group of veteran options, and Michael Saunders is capable of starting games in center field. Jones will need to earn a full-time role to make a mixed-league difference. And if he gets off to a slow start, he could go back to the Minors in short order.

Jon Singleton (10) -- Singleton struggled mightily in 2013, as he dealt with well-documented off-field problems. The 23-year-old spoke frankly during Spring Training, and he indicated that those issues are now behind him. Despite his poor results last season, Singleton entered 2014 ranked as the No. 4 prospect in the Astros' loaded farm system, and his early-season results suggest that he will quickly move into a Major League role. The lefty masher has already totaled 10 homers, 28 RBIs and a .393 on-base percentage in 30 Triple-A games. Houston in last place in the AL West, and the club may soon want to promote Singleton and allow him to develop alongside George Springer this season. Fantasy owners who are thinking about adding Jones should instead sneak Singleton to their bench and wait for a May callup.