Halfway through the NFL season, we’re beginning to see the difference between those who were just slow to start and those who have been disappointing. Of course, there is a difference between players who are disappointing and players who just aren’t very good. In order to be considered disappointing, a player must first have expectations.

Expectations are placed on players for a variety of reasons. Sometimes it is the result of a big contract signing. Sometimes young players show signs of breaking out and becoming a star. Sometimes players already have a proven track record. No matter the reason, expectations are not always met. Here is a list of nine players who have fallen short so far in 2012.

Maybe it’s unfair to ask a player to switch from the Patriots to the Bengals and have the same type of production. But lack of production is only part of the reason why Green-Ellis would land himself on a list of the most disappointing players in the NFL this year. In his four seasons with New England, Green-Ellis never fumbled in 310 rushing attempts. He’s fumbled three times while losing two in only 125 attempts so far this season. His two touchdowns through puts him at a pace well short of reaching the 11 he put up last year or the 13 he scored the year prior. Even at the modest price of his off season contract, the Bengals had to have hoped for more than 3.4 yards per carry.

In the off season, Joe Flacco told reporters that he thinks he is the best quarterback in the league. Yes, a quarterback should probably think that way, but if he’s going to declare it to everyone, that’s the standard by which he should be judged. Too often a quarterback’s record as a starter is mistaken for his ability. Flacco is no exception. Even though the Ravens are 5-2 and are tops in the AFC North, Flacco is outside of the top 10 in quarterback rating, completion percentage, touchdown passes and yards per completion. He also has nine touchdowns to six interceptions and two fumbles. Maybe his comments set him up for disappointment, but he has proven himself to be far from consideration as one of the league’s best.

No list would be complete unless it included a member of the perennially underachieving Dallas Cowboys. Last season, Dez Bryant caught 63 passes for 928 yards and looked poised to become one of the NFL’s premier receivers. But as much as he’s misbehaved off of the field, he’s proven to be as equally undisciplined on it. Whether it has been poor route running, dropped passes or misread coverages, his inconsistent play has caused fans in Dallas nothing but headaches. So far, Bryant has had over 100 yards receiving once while barely showing up for two ghastly sub 20 yard performances. Quarterback Tony Romo is going to have to look elsewhere for a reliable target if the Cowboys are going to make the postseason.

After inking a four year contract extension worth $53.5 million prior to the 2011 season, Johnson has been less than impressive. This is not a list of last year’s most disappointing players, but don’t forget that the deal followed a 2,000 yard rushing season in 2010 and Johnson has yet to put up numbers even close to that. Through the first eight games this season, Johnson has only broken the 100 yard rushing mark twice and has only two touchdowns. That being said, if this list were being compiled next week, perhaps Chris Johnson would be replaced by somebody else. In his last three games, he has gained an impressive 385 yards. With those numbers, he’ll go from one of the most disappointing to regaining his status as one of the very best. Only time will tell.

Before muddying the waters in New York by trading for Tim Tebow, the Jets signed quarterback Mark Sanchez to a contract extension in the offseason that will earn him $58 million over the next five years. Through eight weeks, it’s proving to be money unwisely spent. Sanchez’s 10 touchdowns and eight interceptions have left some fans and media members screaming for him to be replaced by Tebow. No matter who is playing quarterback at this point, the Jets will need a miracle to rescue them from what has been an embarrassing 3-5 start.

After finally enjoying a healthy season in 2011, Stafford showed signs of being the franchise quarterback that the Lions had been lacking. He threw for over 5,000 yards and 41 touchdowns while earning a spot as a probowl passer. Entering the 2012 campaign, he sought to establish himself as one of the game’s best quarterbacks. Through seven games, though, he has been anything but elite. He has thrown only eight touchdowns against seven interceptions while having yet to hook up with star receiver Calvin Johnson. Sunday’s performance against the Seahawks looked promising, but at 3-4 the Lions are looking at an uphill battle to earn a second straight playoff berth.

The Buffalo Bills made the biggest free agent signing of this offseason when they landed Mario Williams. After signing Williams to a six year deal worth $96 million, the Bills thought they were getting a superstar to transform their struggling defense. But after seven games, the Bills D has been dreadful, giving up more than 45 points three times and ranking dead last in total yards given up. While Williams isn’t the only culprit, his 3.5 sacks and 16 tackles fall short of his expected output.

Perhaps the biggest worry for the Eagles heading into this season was the health of their star quarterback Michael Vick. He was removed from two preseason games with injuries to his hand and ribs. After concerns for his health were put to rest, the focus switched to his propensity for giving the ball to his opposition. Through seven games, Vick has fumbled nine times and thrown eight interceptions while compiling only nine total touchdowns. The Eagles fell short of making the playoffs in 2011 after assembling their “Dream Team,” and their fate looks no different this year after struggling to a 3-4 record.

After earning Rookie of the Year honors in his first campaign, expectations for Newton could not have been higher. Whether it’s the pressure to repeat his performance of last season or the opposition learning how to defend him more effectively, Newton has clearly disappointed up to this point of the season. Last year, he set rookie records throwing for 4,051 yards, rushing for 706 yards and scoring 35 total touchdowns, which prompted preseason whispers that he could contend for this season’s MVP award. That expectation is proving to be premature as Newton is well behind pace to match any of his impressive numbers from last year.