Most difficult position to project to the college level? (Football)

I'd say middle linebacker.  You can judge the athleticism easily, but the mentality of the position is very difficult to gauge.  One can be a great athlete but not an overly smart defender and be a fantastic high school MLB, but it takes a lot of smarts to excel at the college level.

QB seems like it must be tough, since a good number of lower ranked guys end up becoming stars (Kaepernick, Kellen Moore, etc. too many to name). And a lot of 5 star QBs never pan out.

Missionary

Got to step your game up at the college level.

it takes longer to grow them physically than any other player out there and the line calls are so specific and varied that  nobody steps in to start and play at a high level as a freshmen.  our most famous lineman excepted of course, but that's what made them famous.    and the transition from h.s. to college is particularly difficult b/c of the speed and size of collge d-lineman and LB's.   thus, the longer the transition and the greater the physical and mental skills needed, the harder to predict regarding success. 

and that's the truth.

Aside from qb, I would say it's the line positions, because there's the added variance of players growing into their bodies. Most college athletes at other positions are already at or near their ideal playing weights, while offensive and defensive line some of them are still getting taller, or have large amounts of weight to gain or lose, and their style of play is so much more physically demanding than most.

Offensive linemen because there's so much physical maturity guys have to go through before they're ready to play. Really hard to project.

Quarterbacks because a lot of the game is mental and it's hard to measure that in high school.

Seems to me that we have had the biggest variance at the safety position. Jordan Kovacs was rated significantly below pretty much all of the safeties we've had over the past decade and has definitively been the biggest contributor of the whole lot.

Didn't we just recently have a diary post about how the QB position is one of the most accurate (aside from RB) from recruiting rankings to actual production?

I project well in whatever position I am in.

I'm curious why you think OL is so surprising, OP?  Because that is certainly it. 

Offensive linemen are the furthest from their college size and strength in high school, making it harder to predict how good they'll be at the next level.  For most positions, high school players are pretty close to the size they'll play at in college, and for the ones who aren't, the recruiting sites often have a hard time assessing them (which is why a guy like Funchess had a rating discrepancy, he needed a lot of bulk for TE and that's hard to predict).  The recruiting sites have an easier time projecting guys who are already college-sized, and that's a much smaller percentage for linemen.  

In addition to the size aspect, OL have to adjust what they do quite a bit from HS to college.  A WR running a route or a LB tackling a RB or a CB covering a pass isn't terribly different from HS to college.  Most linemen, however, are simply much bigger than their opponents in HS and need to learn a lot more technique once they get to college.  

WIth an OL prospect, there are usually two questions a scout asks himself:  Can this huge kid learn the technique to be a good college player? and Can this kid with solid OL technique put on enough mass to see the field in college? Kids who have both of those as a high schooler (like Kyle Kalis) aren't as difficult to scout, but there aren't many of those and 5-stars at any position are pretty easy to scout.  

Because offensive line in high school is such a physical position (with a lack of technique), it's very difficult to view game film and really see how a player is.

On the flip side, when that player gets to college, he has to bulk up, learn technique, learn calls, etc. You don't really know how that drastic weight gain is going to affect their ability to move (pull, pass pro, etc). Also because it's a position based so much on physical maturity and a little less on athletisism, there are probably more late bloomers and successful 2-star O-linemen, whereas a "better" O-line could simply just already be developed in high school and not get considerably better.

Lastly, you have to be a bit nuts to play O-line. I mean, the position itself is exerting your dominance over another 270-330 lbs man. It's very difficult to judge, no matter how much film or interviews or whatever, what an O-lineman's mentality will be once he starts facing guys that are much closer to his size and he has a bit more adversity.

Of course, many of these things can be attributed to other positions, but not to the same degree.

QB would probably be second, because of how fast you have to read coverages and how large and complex the passing playbook is.

you could make a case for CB since very few guys actually play CB in high school

College is a much different game, so there is no telling just how good the kid is with different conditions. So, get some walk-ons, see how well they perform, and give the scholarship to the one that proves himself.

Seems like a position that would have high variability. Lots of people can cherry pick in high school, but it seems like the mental aspect at the next level could be a hard thing to project (like a MLB)

If a kid is already big enough to play the position out of high school, then he likely hasn't developed the technique. Most kids may have the frame, but not the weight. If they have both, then they likely don't have 'good weight' which means that have to drop weight before they can put it back on in the right way.  This added to the general issues you have with kids making the jump from high school to college makes it very difficult to project.

I think the answer is offensive line.  If you look at recent NFL drafts, there are 2-stars and 3-stars and 4-stars and 5-stars in the higher rounds.  Skill positions are easier to project, because it's based on how well you catch the ball, how fast you are, your size, and how quickly you can change direction.  Those things are pretty easy to see live and on film.

2011 NFL Draft:

Tyron Smith: 5-star OT
Mike Pouncey: 4-star OG
Nate Solder: 3-star TE
Anthony Castonzo: 2-star OT
James Carpenter: 4-star OG
Gabe Carimi: 3-star OT
Derek Sherrod: 4-star OT

If you look at that same draft but at skill positions, you see a bunch of consensus studs coming out of high school - Cam Newton, AJ Green, Patrick Peterson, Jake Locker, Blaine Gabbert, Jonathan Baldwin, Mark Ingram.  Most of those guys were the cream of the crop coming out of high school, with a couple "overachievers" like Amukamara and Jimmy Smith - neither of whom has done particularly well in the NFL.  Amukamara is a mediocre starter (2 interceptions in 2 seasons) and Smith is a backup (2 interceptions in 2 seasons).

OL by a mile, then QB or DE.

typo, and you meant DB, right?   i mean, DE's are the biggest knuckleheads on the team (generalizing).  they have to know zero line calls, about 3 plays (twist, dog, zone).   get a good athlete with a good frame, put some weight on him and you've got a college DE.   

Without a doubt it's Quarterback. The speed of the game is so much faster and the defenses are much more complex. In most cases you're asked to run an entirely new system with new terminology. In second place I'd say offensive line. There's a reason a redshirt is 99.9% guaranteed. The size, strength, and speed of the defensive linemen are so much better then the high school level. Most big time oline recruits rely solely on athleticism and their physical prowess to be successful. At the next level they learn so much technique wise, gain muscle weight, and adapt to the speed and schemes that college level ball brings.

Oline, unless the guy has already been in a solid s&c program it's hard to predict how strong he can get while adding the needed weight.. and is he that type of worker.  One reason LTT in this current class was highly rated is he has the athleticism to be elite, but doesn't have the fundamentals, doesn't have near the core strength at all to play for a couple yrs...

QB, it's really a position that can be hard to predict.  Competitiveness, natural leader, very much the has to be preparing more then anyone else type player.  Getting that is so hard...some guys are just better athletically in today's read/spread option run game and start for that reason but the guy that can get the ball where it needs, recognize a defense, blitz, know his routes, route tree vs the coverage and hit it...   That's hard to find a really good qb and develope him.....