Deeeeep sleepers: Carp, Teheran ...

Over the years, the definition of "sleeper" has substantially widened.

Fantasy owners -- even seasoned ones -- these days apply the label to any pick in the later rounds, or any player they think will be drafted later than he should -- including a third-round pick who lingers until, say, the fifth round.

But for the purpose of today's column, let's revert the term to its origins: A true "sleeper" is a player who, almost completely unnoticed at the time of your draft, suddenly becomes a valuable fantasy asset. The point is to identify completely unfamiliar players with the potential to quickly develop into lineup mainstays.

To use the 2012 season as an example, Kris Medlen (31st on the Player Rater), Norichika Aoki (76th), Tom Wilhelmsen (100th), Wade Miley (106th), Ryan Cook (120th) and Tyler Colvin (143rd) would've qualified as true sleepers. They'd have cost you no more than $5 in a singular (AL- or NL-only) league, yet turned in a profit at least as large as that, maybe even double or triple that.

I recognize that a sub-$5 player in an AL- or NL-only league probably won't register on the radar of even a 12-team mixed league. If you're in a shallower format, this list will serve as more of an in-season watch list; I recommend "Tristan's Twenty" as a source of draft-day value selections.

One other caveat: The above represents only six such examples that cracked the Player Rater 150 -- and there are only 250 players drafted in a typical ESPN 10-team standard mixed league -- so the prospects for success with this column's picks aren't great. This is hunting lottery tickets at its purest; the point is that this is supposed to be hard, because the potential payoff is massive. Before even listing a name, I'll guess that half of the picks below fail to turn in 2013 statistics worth at least twice what you paid for them. That's just how this goes.

That said, if even half of them do, their owners will probably win their respective leagues, so long as their "leading men" also perform adequately.

Jake Arrieta, SP, Baltimore Orioles

I discussed Arrieta's skills in greater detail in my "Kings of Command" column, so let's use this space to update his quest for a rotation spot this spring: He tossed four shutout innings of two-hit, five-strikeout baseball without a walk on March 11, then another 4 2/3 scoreless frames March 16. The competition for the Orioles' fifth starter role seemingly has been narrowed down to him, Brian Matusz and Zach Britton. Arrieta's underlying numbers say he's well worth a $1 AL-only bid.

Josh Donaldson, 3B, Oakland Athletics

Donaldson is struggling to get regular at-bats this spring and he no longer brings that attractive catcher eligibility in most fantasy leagues, but his bat possesses a bit more pop than most people realize. Following an August recall, he managed .290/.356/.489 triple-slash rates with a 40.7 percent fly ball rate and 13.8 home run/fly ball percentage in 47 games, eerily similar stats to his .285/.362/.490, 41.0 and 14.0 numbers in Triple-A in 2011 and 2012 combined. Donaldson can also steal a few bases -- he has averaged 12 swipes per 162 games as a pro -- meaning that if he emerges as even a part-timer at the hot corner, he could help AL-only squads.

Jemile Weeks, 2B, Athletics

A bruised right shoulder has cost Weeks some critical spring action -- he hurt it March 1 and returned to game action March 14 -- but he continues to get chatter as a prominent member of the Athletics' second-base battle. A's manager Bob Melvin and hitting coach Chili Davis seem to have nothing but good things to say about the 26-year-old, and Weeks' speed and ability to draw walks makes him a handy AL-only plug-in at a precariously thin position. Even with 300 plate appearances, he could provide a sneaky 15 steals.

Brennan Boesch, OF, New York Yankees

At $1.5 million, Boesch seems a tad pricey pickup for a player who had a .659 OPS last season. But that might convince the Yankees to be more patient with Boesch over the long haul -- remember that someone has to go once Curtis Granderson and Mark Teixeira heal -- and his swing is a good fit for Yankee Stadium besides. Of his 42 career homers, 24 were hit to right field and another 10 to right-center. It's not unthinkable that he could have a Raul Ibanez-2012-like season.

Mike Carp, OF/1B, Boston Red Sox

It's well-known by now that I'm not the biggest believer in Mike Napoli, so it follows that I'd list Carp as an attractive, final-rounds-of-your-AL-only-draft pick. He has always had a bit of pop -- he had a .222 isolated power in 321 career games at the Triple-A level and a .190 mark during his best big league year of 2011 -- and he has balanced platoon splits and the ability to fill in at first base or either outfield corner. He should get at-bats.

Eduardo Nunez, SS, Yankees

Considering the Yankees' many injury woes -- from Alex Rodriguez to Curtis Granderson to Mark Teixeira -- as well as their more frugal approach to roster construction (Kevin Youkilis was really their only big-ticket winter addition), Nunez might play a substantial role for the 2013 team, even if only as a super-utilityman. From a real-game perspective, the team might claim he has a shortstop's bat, which is why they haven't talked him up as a full-time fill-in at either third base or left field. Fantasy owners, however, know that Nunez contributes two useful things: speed, which is handy from a shortstop-eligible player, and the possibility of him picking up additional positions.

Lucas Harrell, SP, Houston Astros

To be clear, he's not going to win many games as a member of the Astros, and his fantasy upside might be that of a matchups specialist, feasting upon the American League's bottom-half offenses. But Harrell has transformed himself into a viable big league starter, thanks to a 2.87 ERA and 7.42 strikeouts-per-nine innings ratio in 15 second-half starts last year, as well as a 56.9 percent ground ball rate in his big league career. Most Astros pitchers aren't worth your consideration; this is the rare one who is.

Rick Porcello, SP, Detroit Tigers

This isn't a misprint: Porcello, who has a 4.59 career ERA, is still only 24 years old, and while he has never developed into the strikeout artist scouts believed he would be, he has nevertheless improved his K rate in each of the past two seasons. He also has improved his ground ball rate in similar fashion. Take note of that second point; it could be significant should he be traded to a team with a stronger infield defense. This is a "last pitcher you buy" pick for AL-only owners, but all the trade rumors make him worth the price.

Evan Gattis, C/OF, Atlanta Braves

A dark horse candidate to make the Braves as a bench bat, Gattis has enjoyed such a productive spring that the team might want to consider him for a 50-50 split of the catching chores with Gerald Laird while Brian McCann recovers from shoulder surgery. A .308 career minor league hitter with .238 isolated power -- that's a .546 slugging percentage, to save you the math -- Gattis has batted .378 with five doubles and two homers in 37 spring at-bats. If he makes the team, this is the kind of low-cost, can't-hurt-you NL-only option I love to slot into my No. 2 catcher spot.

Kyle Blanks, 1B/OF, San Diego Padres

He's my "fantasy kryptonite." I have been unable to resist Blanks' combination of power and walks this past half-decade. That said, if the player is bound to cost no more than $1 in an NL-only league, should one be ashamed to invest? Blanks' biggest problems have been a penchant for strikeouts and injuries; a foot issue mostly ruined his 2010 season and Tommy John surgery his 2011 season, and a shoulder issue entirely ruined his 2012. He has been raking this spring, however, and could make the team as a bench bat, where he might factor in left field long-term should Carlos Quentin get hurt.

Nolan Arenado, 3B, Colorado Rockies

There was more hype surrounding Arenado a year ago, when chatter had him potentially breaking camp as the team's starter last season. After a so-so season in Double-A ball -- .285/.337/.428 rates, 12 home runs -- the buzz subsided, at least until a solid spring that has included a .793 slugging percentage. Arenado might yet be ticketed for Triple-A ball, but he'll probably see time in Colorado this summer, and there are worse places for a rookie to break in than Coors Field. He's a contact-hitting type whom NL-only owners should stash for a couple bucks.

Jacob Turner, SP, Miami Marlins

He's having an awful spring, yes, but one thing Turner has going for him that comparably young arms struggling in March don't have is that he pitches for a team that can afford to be patient. Really, the problem is that his strikeout rate has dropped as he has climbed the competitive ladder; he averaged 7.13 K's per nine in Double-A in 2011 but has only a 5.85 rate thus far in the bigs. Command is the key, as he has a good combination of low-90s fastball, curve and slider, the latter two most likely to restore the strikeout potential he had in the lower levels, if they improve. But at least there's this: Turner's home ballpark is a pitching-friendly one, so if he's a $1 NL-only investment, he might at least warrant matchups consideration in those Marlins Park games.

Julio Teheran, SP, Braves

The Braves' January trade of Randall Delgado practically assured Teheran the team's fifth-starter role, and Teheran's spring has done nothing but cement that status. He has made four starts, all of them superb, and has a 1.50 ERA and 18 strikeouts compared to four walks. Keith Law's No. 6 prospect overall as recently as 2011, Teheran had previously been unraveled by sketchy command and a penchant for home runs, but he's a potential high-strikeout, solid-ERA arm who merely needs to make the requisite adjustments to develop into the front-of-the-rotation arm scouts initially predicted. I'm not about to stray from my strong opinion about him just because he has been so-so in a minuscule sample of big league starts. For $3 to $4, he might be a $10-plus NL-only pitcher.

Mark Melancon, RP, Pittsburgh Pirates

Let's not assume there are any guarantees with new closer Jason Grilli, who is 36 years old and has only five career saves. Grilli should succeed in his new role … but if he doesn't, Melancon is the most logical fallback. You might remember Melancon's miserable start to 2012 as the Red Sox's closer, but the more relevant sample to his 2013 cause was his 37-game, post-demotion stint to conclude the year: 1.05 WHIP, 4.00 strikeout-to-walk ratio and a 63.9 left-on-base percentage that explains his bloated 4.19 ERA.