Which teams will have the best defenses over the next three years?

Former high school teammates and top recruits Patrick Surtain Jr., left, and Tyson Campbell will be doing battle going forward for elite defenses at Alabama and Georgia, respectively. Douglas Jones/Icon Sportswire

After a respite for spring practice, ESPN's future power rankings return like a perfectly timed hit on an unsuspecting ball carrier. That's right: It's time to look at which defenses have the best outlook for the next three seasons.

Alabama topped the defense rankings in 2017, and, after another national title run, Nick Saban's signature unit isn't going anywhere. Along with the SEC, both the Big Ten and ACC are well represented here.

As a reminder, the rankings cover the 2018, 2019 and 2020 seasons. Just because a strong defense returns a lot of senior starters doesn't mean it will rank near the top. Defenses must show strength both now and in the near future. Input from opposing coaches factored heavily into the final order of teams.

1. Alabama Crimson Tide

2017 future defense ranking: 1

Scouting the Crimson Tide: After finally getting healthy, Alabama's defense surged during the playoff. While the Tide certainly will miss mainstays like Minkah Fitzpatrick, Ronnie Harrison, Rashaan Evans and Da'Ron Payne, there's more than enough coming back. After a big finish, lineman Raekwon Davis returns for likely his last season and poses a matchup nightmare for just about any opponent at 6-foot-7 and 308 pounds. "An absolute stud," an SEC offensive coordinator said. If Isaiah Buggs continues to develop as a pass-rusher opposite Davis, Alabama's line could be unstoppable.

Perhaps more encouraging is a linebacker group that should benefit from a season of injury and adversity, as young players such as Dylan Moses and Mack Wilson logged significant playing time. There's now a strong balance of veterans (Anfernee Jennings, Keith Holcombe, Christian Miller) and youth to lead the group for years to come. "What was their weakness last year," an opposing coordinator said, "might be more of an athletic strength [in 2018]."

There are short-term questions with a new-look secondary, as Deionte Thompson, Saivion Smith, Shyheim Carter and others take on key roles. Alabama signed Patrick Surtain Jr., ESPN's top-rated cornerback in the 2018 class, as well as Eyabi Anoma, ESPN's top-rated defensive end and No. 3 overall player in the class.