Five defenses built with the future in mind

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Last week on ESPN Insider, I took a look at which NFL offenses enter 2015 in win-now mode after adding veterans this offseason, and which are getting younger and building for the future. Today, we'll take a look at the same metrics for the defensive side of the ball.

Once again, we're going to be analyzing teams using Football Outsiders' snap-weighted age metric, which measures the average age of the players on a team based on which players actually played that season. A player with 1,000 snaps counts twice as much as a player with just 500 snaps. This offseason, for the first time, we decided to create an approximate snap-weighted age estimate for each offense and defense. We analyzed projected starting lineups and created formulas to project the average number of snaps played by lower-round picks based on position. Of course, we can't predict where injuries will force teams to start rookies and other young players. But by looking at where teams added free agents and where they drafted rookies, we can get an idea of which offenses and defenses are building the future and which want to win now.

A reminder: Getting older or younger doesn't necessarily make a team better or worse. (Older teams do perform slightly better based on Football Outsiders' DVOA metrics, but it's a small correlation: 0.15 on offense and 0.17 on defense.) With that in mind, let's look at the five defenses that are built with the future in mind. (You can find the five defenses that are built to win now here.)

All player ages listed below are for 2015, based solely on birth year.

New York Giants

2014: 27.6 (fifth-oldest) / 2015, estimated: 26.2 (27th)

The Giants' defense has been very old for the past few years, in part because they've gotten so little out of recent defensive draft picks. Only two of the defenders drafted since 2011 have started at least eight games in a season: cornerback Prince Amukamara (26) and defensive tackle Johnathan Hankins (23). The Giants have had to fill the holes with veteran free agents. But the Giants find themselves in a better position this season; veterans signed this offseason are a little younger than those from years past -- linebacker J.T. Thomas is 27, lineman George Selvie is 28 -- and this year's rookies should be getting playing time right away.

The biggest part of the Giants' youth movement comes in the secondary. Antrel Rolle (33) will be replaced by second-round pick Landon Collins (21). In fact, last year, three Giants DBs -- all over the age of 28 -- played 40-plus percent of snaps. And all three will be gone this year: Rolle, Zack Bowman (31) and Quintin Demps (30). The return of injured linebacker Jon Beason (30) should be balanced out by an increase in snaps for second-year player Devon Kennard (24). With defensive linemen Mathias Kiwanuka (32) and Mike Patterson (32) both gone, the Giants hope the new blood will help them get back on track. After finishing a very surprising sixth in Football Outsiders' 2013 defensive ratings, Big Blue plummeted to 24th last season.