So how does the industry define an ace? Is in on a performance level? A scouting level? Some combination or both, or something more esoteric? “I think every team has an ace,” said one American League Scouting Director. “There is someone on the staff who is a leader both on and off the field, but I don't think ace necessarily equates to No. 1 starter.”

Defining true aces who are both staff leaders and No. 1 starters proves to be more difficult. “They have to be able to lead a championship level staff,” explained another AL scouting executive. “They have to contribute to winning games every fifth day, to shutting down lineups every fifth day.” To do that takes special talent, and you can't be special without tools. “To be an ace, and sustain that title, it's about the stuff to dominate and overmatch opponents,” he continued. “I'm talking about 7s and 8s on the scouting report [referring to the 2-to-8 or 20-to-80 scouting scale].”

In researching aces, I noted that there is nearly no such thing as a “surprise” ace. When you think about the elite starting pitchers in baseball, you are talking about players who were seen as potential aces as prospects. The only exception at this time is Cliff Lee, who was seen more as a third starter when coming up through the Cleveland system. The other recent surprise ace is Johan Santana, who it should be noted is also left-handed.

So who are the future aces? Here are seven names to keep in mind; remember that aces are without question the most special commodities in the game, and even if just one of these players turns into that year-after-year Cy Young candidate, that might be exceeding expectations.

The Best Bet
Julio Teheran, RHP, Atlanta Braves
Teheran may have not looked like an ace during his two big-league starts, but keep in mind that he was deemed ready for some spot starts as a 20-year-old. When Tim Lincecum was the same age, he had just finished a freshman year at the University of Washington that included 82 walks in 112 1/3 innings. Josh Beckett was dominating as a 20-year-old… in the Low-A Midwest League. For scouts looking for the big numbers on a scouting report, Teheran has been at his best since returning to Triple-A; in five June starts, he has a 1.00 ERA over 36 innings, allowing 20 hits, and walking just two. His mid-90s fastball and plus-plus command are both ace-worthy, while his changeup is an above-average pitch and his breaking ball is showing signs of becoming one. He could be six to eight years away from his peak, yet ready for a full-time role in a big-league rotation next year.

Could Get There with Some Adjustments
Gerrit Cole, RHP, Pittsburgh Pirates
Let's assume Cole is going to sign; the Pirates did not use the first pick on a player they are not going to get a deal done with. The second his deal is done, Cole arguably has the best stuff of any prospect in the game. If you see him on the right day, his mid- to upper-90s fastball is an 80 pitch. Scouts spent many hours this spring arguing over which of his plus-plus secondary pitches was better—the slider or the changeup. That said, he was consistently out-pitched this year by teammate Trevor Bauer, who went to Arizona two picks after Cole. The problem has been command, but with just a few refinements in his location and pitch sequencing, Cole could be a franchise-changing overpowering starter.

Shelby Miller, RHP, St. Louis Cardinals
After finishing the 2010 season with a flurry at Low-A Quad Cities, the Cardinals considered sending their 2009 first-round pick to Double-A at the beginning of the year. Instead, Miller earned the promotion by striking out 81 batters over 53 innings in nine Florida State League starts before moving up. The Texas League has yet to slow him down; he has a 1.69 ERA in his first five Double-A starts. Miller is a classic power arm from Texas with 94-95 mph heat, a very good curve, and an improving changeup, but for now, his 7-6-5 arsenal (plus-plus fastball, plus curve, average changeup) is more reminiscent of San Francisco's Matt Cain than that of a pure ace.

Matt Moore, LHP, Tampa Rays
If being an ace means overpowering opponents, Moore has you covered. He's led the minor leagues in strikeouts over each of the last two years, and is among the leaders again this season with 107 punchouts over 82 2/3 innings for Double-A Montgomery, including 11 in a no-hitter he fired two weeks ago. His 92-95 mph fastball is well above average for a left-hander, and his power curveball is among the best in the minor leagues. While control has been a problem for him in the past, his ratio of 2.5 walks per nine innings in 2011 is a decrease of more than 30 percent from the previous year, which was 25 percent lower than the year before, so the progress in that department has been both clear and consistent. His dominating performances of late have accelerated his timetable, and he could be the recipient of some intense scrutiny for a starting job next spring.

Longshots to Dream on
The lower levels of the minors are loaded with strong arms, as kids light up radar guns while still in the transitional phase from thrower to pitcher. Here are three exceedingly inexperienced arms with some of the highest ceilings one can find, but the caveat remains: aces are rare—incredibly rare—and chances are good none of these players ends up as one.

Carlos Martinez, RHP, Cardinals: Martinez created a stir last summer when he touched 100 mph in the Dominican Summer League while putting up a 0.76 ERA. He's been nearly as impressive in his stateside debut with a 2.33 ERA in eight starts for Low-A Quad Cities to go with 50 strikeouts in 38 2/3 innings. In possession of one of the minor league's fastest arms, there's no debate as to the quality of his fastball, but his curveball and changeup are still works in progress, and his small (6-0, 165) frame leaves many to wonder if he's the type of pitcher that can handle a 220-inning workload.

Jameson Taillon, RHP, Pirates: Taillon, the second overall pick in last year's draft, passes any scouting sniff test with a combination of mid-90s heat and fantastic control. He's walked just four batters in his first 42 2/3 innings for Low-A West Virginia, but he's also been more hittable than expected as he learns how to set up hitters and integrate the rest of his arsenal into his game.

Taijuan Walker, RHP, Mariners: Still just 18 years old, the Mariners’ 2010 supplemental first-round pick exploded onto the Low-A Midwest League in May and has recorded 64 strikeouts in just 50 innings. Arguably the most athletic pitching prospect around, Walker is already throwing in the 95-98 mph range and showing flashes of an excellent breaking ball, but his changeup is still in the nascent stage, and his control is erratic at best.  


A version of this story originally appeared on ESPN Insider Insider.