Project players come in all shapes and sizes. Sometimes it is a speed demon wide receiver or defensive back that lights up the combine, but really doesn't have a refined skill set. Other times it is a guy that was extremely productive in college due to technique, but who doesn't have the ideal measurables for the NFL. Lately however there has been a trend of players that have been big and athletic that have made the conversion to tight end, whether they started out as defenders, wide receivers or basketball players. These three Titans players came in with the same sort of upside, and they are running out of time to prove that they can develop into real NFL players.
People forget that last year Campbell reportedly almost beat out Alterraun Verner for the second cornerback job. Campbell has the speed and physical tools to be a dominant corner in the league, but his play on the field hasn't been inspiring. If Ray Horton can come in and teach him how to actually play up to his potential then the Titans will have no issues at CB this season. If not, then this may be the end of the road for a player who could get lost in a crowded secondary competition.
In Mariani's first year he showed great patience and vision as a special teams player, and looked like he could have some potential as a future slot wide receiver. Unfortunately, two major injuries have derailed his career and now both spots have been filled. Can Mariani prove that he is more than just a good return man and show some ability as a tackler on special teams? Barring that he would have to prove that he can be a high-quality depth receiver in this group or else he could be in St. Louis next season (we all know the deal).
Thompson is a converted defensive end, so when he didn't explode in year one it wasn't a huge shock. However, after hearing about his potential for a few years and him getting multiple opportunities to separate himself as the top move-FB/#2 TE, he has lost his spot to Collin Mooney. Mooney was injured at the end of last season, and in the new Whisenhunt offense I expect to see two tight ends on the field a lot more often than a running back and a fullback. With that in mind plus Jason Michael's affinity for developing tight ends, this is the best possible situation for him. If he can't thrive on offense this year, it may be time to think about switching him back to defense or using him purely as a special teams player.