Mike Trout again finds himself in the thick of the American League MVP debate. (Stephen Dunn/Getty Images)

As the past two Septembers approached, the American League MVP race provided a backdrop for the kind of debate that pervades modern baseball. In 2012, for instance, Detroit’s Miguel Cabrera led the majors in batting average, home runs and RBI, becoming the first player since Carl Yastrzemski in 1967 to win what has long been known as a hitter’s “Triple Crown.”

Statistics, now, are valued differently, and both batting average and RBI are less important in most analyses than they used to be. So a vocal argument grew in support of Mike Trout, the young center fielder for the Los Angeles Angels of Anaheim, who in both seasons beat out Cabrera in WAR – wins above replacement, the stat that tries to quantify not only hitting but base running and defense, then turns it into the number of wins that player provides a team relative to a minor-league call-up.

I still remember, in the postseason of 2012, Frank Robinson – a Triple Crown winner himself – being asked whether Cabrera or Trout should be the MVP. Robinson was incredulous. A guy leads his league in average, homers and RBI, and his team made the playoffs? How could he not be MVP?

But these are different times.

Cabrera is having, by his standards, a down year, in part because he has been battling injuries. His on-base plus slugging percentage is a solid .888, but that’s down 190 points from a year ago, and his .517 slugging percentage is his lowest since 2004, his first full major-league season. So that leaves the door wide open for Trout to walk through. A look at the race as it heads for the homestretch.

NL MVP Shortlist | MVP debate needs more than WAR

Mike Trout, CF, Los Angeles Angels of Anaheim

The case for: Is it possible that a 23-year-old in the midst of his third full major league season is about to receive a lifetime achievement award? Maybe. Trout’s season has been excellent. He leads the American League in both runs scored (99) and driven in (103). According to FanGraphs, his WAR is a league-best 6.9 – nearly a full win, at this point, over the next best player, Kansas City’s Alex Gordon (6.0). He’s third in slugging percentage (.554) and fourth in OPS (.926), has a career-high 32 homers, plays a premium defensive position, and the Angels are surging to a division title. There is a sense that, after being nudged out by Cabrera in consecutive years, it’s Trout’s time.

The case against: Is Trout about to be rewarded for a season in which some of his numbers are down — markedly? After hitting .326 and .323 in his first two full seasons, he’s down to .288 this year – which has, in turn, dragged his on-base percentage down a full 60 points from last year, from .432 to .372, and his OPS down from .988 to .926. His strikeout rate is up (25.5 percent, from 19.0 percent in 2013) and his walk rate is down (15.4 percent in 2013, 11.4 percent this year). FanGraphs’ ultimate zone rating (UZR) would say he’s having a down year in center field, though that metric is better used over a period of seasons and can be faulty in a smaller sample size. He is, though, less of a threat on the basepaths; after stealing 82 bases from 2012-13, he has just 14 steals this year.

Victor Martinez, DH, Detroit Tigers

The case for: At 35, the Detroit Tigers’ designated hitter is enjoying his best season. He’s the only AL player with an OBP above .400 (.406), is slugging .571 (second only to White Sox rookie Jose Abreu) and has a league-best .977 OPS, the best of his career. He could, too, win a batting title; at .335, he trails Houston second baseman Jose Altuve by just a point in a race that could go down to the final weekend. Throw in 30 homers and 96 RBI, and the fact that the Tigers are clinging to a playoff spot, and this is a legitimate candidacy.

The case against: The two words listed as Martinez’s primary position – designated hitter – likely hurt the most. Because he contributes very little defensively (31 appearances at first base and two as a catcher, with 102 games as the DH), his WAR suffers. In FanGraphs’s version, he ranks just 19th in the league. And even in baseball-reference.com’s version of offensive WAR, Martinez – hindered by below-average base running — places just eighth in the league at 5.0, well behind Trout’s league-leading 7.6.

Alex Gordon, LF, Kansas City Royals

Alex Gordon’s advanced metrics shine far brighter than his traditional stats. (Lon Horwedel/AP Photo)

The case for: This is almost completely built on modern analysis, which gives the Kansas City left fielder credit for being outstanding at his position. FanGraphs’s version of WAR puts Gordon behind only Trout in the AL Gordon has also been the best offensive player on a Royals team that is contending to end the majors’ longest playoff drought, something that could strike a chord with more traditional voters. Gordon leads the power-deficient Royals in homers (19), RBI (66), runs scored (77), slugging percentage (.447), OBP (.354) and OPS (.802).

The case against: Just look at Gordon’s slash line: .272/.354/.447. Is that MVP-caliber? He’d have to be a darn good left fielder to thrust himself ahead of Trout or Martinez with those offensive numbers. It’s a good-but-not-great year.

Josh Donaldson, 3B, Oakland Athletics

The case for: If Gordon is a contender, shouldn’t Oakland’s third baseman be, too? Donaldson’s slash line of .257/.345/.459 might not seem MVP-worthy, but he leads baseball-reference.com’s version of WAR at 7.1, better than even Trout. His 26 homers, 93 RBI and 85 runs scored all put him ahead of Gordon, too.

The case against: As the A’s have inexplicably struggled since the July 31 non-waiver trade deadline, Donaldson hasn’t helped make up for the trade of power-hitting outfielder Yoenis Cespedes. Before driving in four runs with five hits in a win Tuesday night, he had just 13 RBI and 12 extra-base hits in his previous 35 games as Oakland’s grip on a postseason spot grew more tenuous.

Felix Hernandez, P, Seattle Mariners

The case for: No American League starting pitcher has done more to get his team into playoff contention than Seattle’s ace lefty. He leads AL pitchers in both versions of WAR, has the league’s best walks-and-hits per inning pitched (0.915), is in a heated battle with Chicago’s Chris Sale for the ERA title (trailing now, 2.09 to 2.12, which is the best of his stellar career), has already thrown 212 innings (trailing only David Price’s 219). Hernandez’s best stat: He has allowed two or fewer earned runs in 25 of his 30 starts.

The case against: As insane as it seems, some voters could still point to Hernandez’s win total – only 14, with no way to get to the old benchmark of 20. A more reasonable argument would be that starting pitchers shouldn’t be strongly considered for the MVP award given that they play less than a fifth of their team’s games. And for even those inclined to include a starter, is Hernandez’s season – not historic, by any measure – worthy of the kind of consideration Dodgers lefty Clayton Kershaw will get in the National League?