If there is a weakness in David Harris' game, it is playing pass coverage. He is not very fast and has trouble staying with athletic players over long stretches. His ball recognition skills are also somewhat lacking. Think Matt Spaeth catching a touchdown right in front of him Week 15 in Pittsburgh.
How much did this really hurt the Jets this season, though? Harris primarily played over the middle, where secondary receivers run crossing routes and tight ends try to stretch the field. Football Outsiders studied every play and have the Jets ranked 9th against tight ends and 11th against receivers third and lower on the depth chart. These aren't elite numbers, but they are in the top half of the league.
Opponents completed over 70% of passes targeted at him for a rating of over 100. The thing is there are not many great cover linebackers in football. Pro Football Focus says 33 other inside linebackers gave up a 70% completion rate. 23 linebackers had a rating over 100. 20 linebackers allowed more yards in pass defense, which is striking since Jets opponents were more likely to target the middle with Darrelle Revis and Antonio Cromartie on the outside.
Harris is not good in coverage, but the team can live with it. Most teams have to scheme around it. The Jets have done so.