Red Flags: AFC West

Joe Mays struggled at middle linebacker last season for the Denver Broncos. Will he start this season? Jim Rogash/Getty Images

Welcome to the 2013 version of Insider's offseason staple series: Red Flags. This is the fourth of an eight-part examination in which Football Outsiders identifies the biggest remaining issue for every NFL team, division by division, after the NFL draft.

The series continues Thursday with Outsiders' look at the AFC West.

Denver Broncos: middle linebacker

In our last installment of this series, we chronicled the Broncos' need for interior run defenders. Since that time, the Broncos have been able to re-sign Kevin Vickerson, add Terrance Knighton and draft Sylvester Williams -- three essential cogs to stopping the run near the line of scrimmage. On the linebacker front, however, Denver hasn't been nearly as proactive.

In 2012, Football Outsiders ranked Denver's rush defense among the league's best. They were fourth overall in run defense by Football Outsiders' DVOA (defense-adjusted value over average) metric, as well as third in second-level yards and first in open-field yards. The last two metrics show how productive Denver's linebackers and the secondary are at stopping the run once it breaks into the second level. To add further evidence, Denver's defensive adjusted line yards (ALY) for runs directed between the guards ranked sixth in the league.