Not so easy to pick a Heisman winner

Lenn Robbins

ROBBINS' NEST

The envelope has been sitting on my desk for about week now, and I’m convinced it’s a poltergeist. Each time I push it to the side, the ballot returns to my line of sight.

I’m not opening it until Monday, the day Heisman Trophy ballots are due. Here’s a closer look at the candidates, and why I’m waiting:

Matt Barkley, QB, USC: Carson Palmer won the Heisman. Matt Leinart won the Heisman. And Barkley is having a better season than either former Trojan, on a team that was banned from playing in a bowl game and not eligible to win its league title.

Barkley has had two six-touchdown games and neither were against Hawaii. After Barkley led USC to an upset victory at Oregon, Ducks coach Chip Kelly said he was the best quarterback in the Pac-12.

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FEELING LUCK-Y: Stanford’s Andrew Luck is one of six legitimate Heisman Trophy candidates, says The Post’s Lenn Robbins, who has yet to return his Heisman ballot.

At 6-foot-2, 220 pounds, Barkley has a smile as big and wide as the HOLLYWOOD sign and blond hair a surfer dude would trade a big wave for. If he’s the best QB in the Pac-12, he’s a legit candidate.

Justin Blackmon, WR, Oklahoma State: If you have any questions about why Blackmon is considered a top-five pick in next year’s draft, tune into today’s Bedlam game against Oklahoma. If No. 81 doesn’t jump off the screen, you need to watch another sport.

The 6-foot-1 1/2, 215-pound Blackmon is the first wide receiver in Big 12 history to win the league’s Most Valuable Player award. Yep, a wide receiver. Desmond Howard, anyone? Legit Heisman candidate.

Robert Griffin III, QB, Baylor: He has had more big moments, more Heisman moments, than any player in college football. The Bears have three losses, but without Griffin they might not have any wins.

Griffin, who leads the nation in total offense and scoring, has completed 72 percent of his passes for 3,678 yards and 34 touchdowns. While getting bored slicing up defenses, he has amassed 627 all-purpose yards. Legit Heisman candidate.

Case Keenum, QB, Houston: He’s having a season for the ages, capping a career for the ages. Keenum is college football’s career total offense leader and leads one of just two undefeated teams in the nation. This stat is almost inhuman: Keenum has attempted 467 passes and thrown just three picks, on the way to tossing 43 TDs.

Here’s what makes Keenum’s season flat-out mind-boggling. He did it after recovering from reconstructive knee surgery. Before critics complain about the level of competition Houston faces or the Cougars’ style of play, consider this: Keenum has finished just three games — no stat padding. Legit candidate.

Andrew Luck, QB, Stanford: Luck is the college quarterback NFL scouts have the most love for — we’re talking Valentine’s Day love. He will be the first player taken in next year’s draft. The Colts are thinking of using the No. 1 pick, if they remain winless, to take Luck, making Peyton Manning (gulp) expendable.

Luck was the leading Heisman candidate coming into the season and has done nothing to disappoint. He has thrown 35 touchdowns and nine interceptions and led Stanford to an 11-1 record. Legit Heisman candidate.

Tyrann Mathieu, CB/PR, LSU: “Honey Badger” is the best player on the nation’s best team. Mathieu is averaging 13.6 yards per punt return and returned one for a touchdown to break Arkansas’ back. His fumble recovery returned for a touchdown broke Oregon’s. When LSU needs a play, Mathieu has delivered.

He has returned two fumbles for touchdowns. He has 66 tackles, 11.5 tackles for losses, 1.5 sacks, two interceptions, seven passes defensed, six forced fumbles, the funkiest honey-colored hair you’ll see outside of the East Village and the best nickname in the modern era of college football. Legit candidate.

Trent Richardson, RB, Alabama: When Mark Ingram won the Heisman two years ago, many believed Richardson was the best running back on the team. He used his final game against Auburn to leave a last impression, rushing for 203 yards.

This season, he has emerged as a receiver, catching 27 passes for 327 yards and three touchdowns. He’s the best offensive player in the SEC, the nation’s best league. Legit Heisman candidate.

Now you know why the envelope hasn’t been opened. Six candidates, six great candidates, for three spots. The Post invites you to vote. We’ll announce the results next Saturday, the day the Heisman is presented in the city, along with my vote.

lenn.robbins@nypost.com