The Ravens could have as many as seven or eight new starters on defense when the 2013 season begins. You can produce a number of statistics that suggest why they may have felt compelled to overhaul their defense.

Here is a good one: The Ravens whiffed on 87 tackles during the 2012 season, according to Football Outsiders.

Aaron Schatz, who wrote about broken tackles in this recent post, explained that Football Outsiders define a broken tackle as one of two events: “either the ball-carrier escapes from the grasp of the defender, or the defender is in good position for a tackle but the ball-carrier jukes him out of his shoes.” Schatz added that “if the ball-carrier sped by a slow defender who dived and missed, that didn't count as a broken tackle.”

Based on Football Outsiders’ charting, done by more than two dozen people, only three NFL teams missed more tackles during the regular season. Opposing ball-carriers broke a tackle on 76 of Baltimore's 1,077 defensive snaps. With at least one missed tackle on 7.1 percent of their plays, the Ravens defense was third-worst in that category.

Free safety Ed Reed, who has since signed with the Houston Texans, was their worst offender. According to Football Outsiders, he missed 15 tackles, the second-highest total in the NFL. And his broken-tackle rate of 22.7 percent appears to be the highest among qualifying players.

A pair of Ravens inside linebackers also struggled, ranking among the highest at the position in broken-tackle rate. Jameel McClain missed seven tackles for a broken-tackle rate of 10.6 percent. Dannell Ellerbe, now with the Miami Dolphins, wasn't far behind with a broken-tackle rate of 10.1 percent with eight missed tackles.

That trio combined for a third of the team’s missed tackles.

After a rocky start to the 2012 season, the Ravens defense played better in the season's second half. The Ravens finished the season ranked 12th in scoring defense, 17th in total defense and pass defense, and 20th in run defense. The defense gave up just 43 points in their first three playoff games before the San Francisco 49ers scored 31 points in Baltimore's 34-31 Super Bowl victory.

But even in the playoffs, Ravens defenders continued to let ball-carriers slip out of their grasp. Football Outsiders charted the Ravens with 28 broken tackles in their four playoff games, including 13 against the 49ers in the Super Bowl. Reed missed three tackles in the Super Bowl alone.

The broken tackles weren’t the sole reason the Ravens decided to rebuild their defense. But they pride themselves in being a unit that finishes off plays. Too often they failed to do that in 2012.