Every season, a handful of erratic rookies find themselves smack in the midst of a major league playoff race. And every year, many of them crack under the pressure and humbly learn that they aren’t bigger than the game.

Rookie starters on winning teams are especially scrutinized, which often conveniently overlooks the fact that they are physically tired after the largest workloads of their young careers. Yankee fans get a reminder of the physical toll put upon young pitchers each time Jaret Wright takes the hill; in no way does he resemble the pitcher he was in 1997.

But this year, some of the most important pitchers on American League contenders are actually rookies (or, in one case, a second-year player in a veteran-heavy lineup). These teams wouldn’t be where they are without the following young pitchers, who in some cases earned their jobs by displacing a veteran. To get a feeling for how good these young pitchers have been this season, we’ll use Value Over Replacement Player (VORP), a Baseball Prospectus metric that measures how many runs a player is worth over a freely available alternative.

FRANCISCO LIRIANO (MINNESOTA)
26 G, 115 IP, 51.7 VORP

If you felt a great disturbance in the force sometime Monday evening, here’s why: Liriano was removed from his start against Detroit after just four innings and 67 pitches. One of the most exciting and promising young pitchers in the game, Liriano’s emergence is a very big reason as to why the Twins have been able to claw their way back into Wild Card contention after a slow start.

Currently, though, he’s perhaps the only member of this group whose season may get written about in the past tense for the rest of the year.Nearly in tears after pointing to the inside of his elbow, where he was experiencing some pain, he’s now reportedly headed to the disabled list with what manager Ron Gardenhire has called a forearm problem.

Liriano was broken in slowly, as teammate Johan Santana was, using an extended stint in long relief to give him some experience while depressing his workload. With Santana, it arguably went on too long, but it did ultimately protect his arm. With Liriano, a converted outfielder, the Twins may have not used enough caution.

The Twins are actually blessed with young options to fill in the rotation should they be without Liriano for longer than 15 days. Though as good as young prospects Matt Garza and Scott Baker may be, they don’t project to be nearly as good as Liriano, who was second in the majors in VORP. The Twins’ Wild Card hopes are in trouble, but without Liriano, it’s likely they wouldn’t have Wild Card hopes to begin with.

JOHNATHAN PAPELBON (BOSTON)
49 G, 56.7 IP, 35.0 VORP

His is the kind of statline normally reserved for an exaggeratedly good player you created on PlayStation baseball (and happened to name after yourself).In his 56.7 innings this year, Papelbon has 58 strikeouts against 10 walks, and has surrendered just 29 hits. This has all helped to keep his ERA at a microscopic 0.64.

While Boston is having some pitching trouble, the ninth inning has been pretty free of drama, Sunday night’s home run to Dioner Navarro notwithstanding. Papelbon’s ERA jumped from 0.61 up to 0.64 after that game, giving him just four earned runs on the entire season, three of which came off solo home runs. His VORP of 35 ranks him 23rd in the majors among all pitchers, and he’s the highest reliever on the list.His splitter isn’t quite the trick pitch that Tom Gordon’s power curve once was, but Boston fans are once again getting used to opposing batters looking foolish on offspeed pitches in the late innings.

JUSTIN VERLANDER (DETROIT)
21 G, 135.3 IP, 47,8 VORP

The Tigers passed up Rice University’s Jeff Niemann, Phil Humber, and Wade Townsend in 2004 to take Verlander second overall in the amateur draft. They also passed on the Angels’ Jered Weaver, so it’s safe to say they thought differently about Verlander than many other teams, who thought he was, at best, the fourth- or fifth-best pitcher in that draft class. But Verlander has been terrific for Detroit — he’s currently tied for first in the majors in wins, and has the second-lowest ERA (2.74) among major league starters.

Detroit is being cautious with him as the season winds down, particularly since this is the second year in a row arm fatigue has interrupted his season. He has already set a career high in innings pitched, and Detroit had him skip a start last week to help ensure his late-season health. And why not? Detroit’s lead is large enough (10 games before last night’s action) where they can start to think about keeping players healthy for the playoffs. Although veteran Kenny Rogers started the All-Star Game, they wouldn’t be where they are without the emergence of Verlander.

CHIEN-MING WANG (YANKEES)
24 G, 156.0 IP, 40.5 VORP

Wang isn’t a rookie, but his place on this list makes sense when you consider a number of factors. For one, the Yankees’ farm system is oft-maligned for not producing much, if any, decent major-league talent lately. Wang is a homegrown pitcher who also happens to be just off the team lead in VORP among pitchers (Mike Mussina has 40.9,though in slightly more innings pitched).

The second thing is that Wang’s strikeout rate is the lowest among current starters with more than 150 innings pitched. Liriano and Papelbon are well above the league’s average strikeout rate, Verlander’s about average, and Wang’s is significantly below, which is not a metric usually associated with dominance.As long as Wang relies on his defense to record the majority of his outs, he’ll be walking a very fine line.

Even though this represents a red flag for his future success, that doesn’t take away from his current success, and he’s had a tremendously successful year. All things being equal for Wang, he’s one to watch for Cy Young consideration — by advanced metrics, he’s not near the top of the list, but by the more traditional baseball metrics (Wins, for one), he should rank right up there with the rest of the contenders, as his 13–4 record looks to take advantage of an improved offense down the stretch.

Mr. Erhardt is a writer for Baseball Prospectus. For more state-of-the-art analysis, visit baseballprospectus.com.