When you hear the term "base defense," what do you picture? Chances are, if your favorite team plays a 4-3, then you picture four defensive linemen, three linebackers and four defensive backs. If your favorite team plays a 3-4, then you picture three defensive linemen, four linebackers and four defensive backs.

Here's the thing, though: no matter which set your favorite team plays out of, you're picturing the wrong thing. That's because the nickel defense has taken over the NFL. Here, via Peter King at The MMQB, is the evidence.

The 2015 season was the seventh straight year for an increase in the number of defensive snaps in the NFL with five defensive back or more on the field. Per Pro Football Focus here is the percentage of plays in NFL games with five DBs or more on the field in every season since 2008:

2008: 43.4%

2009: 45.1%

2010: 48.8%

2011: 52.5%

2012: 54.4%

2013: 58.3%

2014: 60.3%

2015: 63.4%

Nearly two-thirds of all snaps were played in the nickel defense last season, so it's about time we start referring to sets with five defensive backs as the base NFL defense. The rise of slot cornerbacks and hybrid safety/linebacker types has coincided with the proliferation of spread offense concepts throughout the NFL. Offenses are turning to more one-back sets, more three-wide sets, and more shotgun with each passing season, and defenses have predictably responded by putting additional coverage players on the field.

King puts forth this trend as reason the Titans could opt for Florida State corner/safety Jalen Ramsey with the No. 1 pick in this month's draft over Ole Miss tackle Laremy Tunsil (if they don't trade the pick to a QB-needy team).

The NFL, as the Pro Football Focus numbers show, has transitioned into more of a three-down passing league. Ramsey had only three interceptions in the past three college seasons at Florida State, but he seems the most pro-ready corner in this draft. He’s a 6-1, 210-pound specimen with the ability to cover the kind of big receivers the league is fielding today. He can play cornerback, he can move inside and cover the slot receiver, and he can play a center-field kind of safety if need be. He’s the kind of versatile defensive back every coach wants. The Titans have a crying need at tackle, after allowing more sacks than any team in football last fall. But they also need a corner and a nickel defender as well, and defensive coordinator Dick LeBeau would froth at the chance to use a player with the blitzing and tackling skills of Ramsey.

So … do not assume Tennessee is locked into Tunsil. Robinson certainly could take him. But the top of the draft is in flux, and I will not be surprised if in the next three weeks the Titans move the pick for an extra high pick or picks—even though there’s not the Andrew Luck or Marcus Mariota out there to move up and grab. But there are teams like San Francisco or Los Angeles or Philadelphia that might want a quarterback, and might be desperate enough to overpay for the top pick.

Ramsey is widely considered the top defensive back in the draft, and in some circles has been mentioned as the best defensive player or even best overall player available. The Titans could certainly choose to go in that direction, even if Tunsil seems more likely. If Ramsey does go No. 1, he would be the first DB picked in that spot since 1956.

Could Jalen Ramsey go No. 1 overall? (USATSI)