The NFL is feeling its usual quarterback shortage even more acutely now that injuries have sidelined three of the nine highest-ranked starters from our 2015 QB Tiers survey. With Ben Roethlisberger, Drew Brees and Tony Romo on the mend and Peyton Manning nearing the finish line of his career, the league needs unproven young prospects to make big jumps forward.

Derek Carr, anyone? The 35 coaches and personnel evaluators polled for the QB Tiers project consistently pointed to the Oakland Raiders' 2014 second-round draft choice as the first- or second-year quarterback most likely to reach the highest tier. They liked Teddy Bridgewater and offered mixed reviews for Jameis Winston. They were generally positive on Marcus Mariota without projecting stardom for him. The feeling on Blake Bortles was lukewarm.

Carr was in a separate, higher category despite a brutal rookie stat line, as he landed at No. 20 overall after just one season. So far it looks like the evaluators are onto something. The first three games of the 2015 season have Carr trending in the right direction, with good numbers and even the highest of compliments from a teammate, making this a good time to revisit the reasons league insiders were so high on him. But let's not anoint him yet. Insights from a veteran defensive coach who studied Carr this season point to one key area where the QB must improve.