Los Angeles Rams' 2018 free agency: Center John Sullivan keeps O-line intact

Center John Sullivan will return to the Rams for a second season. Mark J. Rebilas/USA TODAY Sports

A breakdown of the Los Angeles Rams' 2018 free-agent signings:

John Sullivan, C

The Rams no longer have to worry about center. They brought back veteran John Sullivan with a two-year contract that is worth up to $15 million. Here’s a closer look at the signing:

Grade: B. Sullivan made only $999,999 last year, so he earned a big raise. But not that big. Sullivan’s contract will basically only reach $15 million if he plays in every game and the Rams do well in the playoffs, according to a source. It’s more like a two-year, $10 million contract with incentives and some protection against injury.

What it means: It means the Rams’ highly successful offensive line returns intact, with Andrew Whitworth and Rob Havenstein serving as the tackles and Rodger Saffold and Jamon Brown returning as guards. Sullivan was graded 10th among 36 centers by Pro Football Focus last season because of his blocking. But he was also a major asset for young quarterback Jared Goff because of his familiarity with Sean McVay’s offense and his ability to identify coverages before the snap.

What’s the risk: Sullivan will be 33 on Aug. 8, and he missed the entire 2015 season because of back issues. Yes, there are risks involved with this. But the Rams prepared for it in the framework of this deal. The second year of Sullivan’s contract comes with a low guarantee, with most of the money coming in per-game roster bonuses. Sullivan didn’t miss any starts because of injury last season, but the Rams know they can’t necessarily count on that again. They hope Austin Blythe continues to develop into a solid backup.

Nickell Robey-Coleman, CB

The Rams checked an important, under-the-radar item off their to-do list when they brought back slot corner Nickell Robey-Coleman with a three-year contract on Tuesday. The deal is worth about $15.75 million with $8 million guaranteed, according to NFL.com. Here’s a closer look at the signing:

Grade: B-plus. Robey-Coleman, listed at 5-foot-8 and 178 pounds, is a little undersized for the outside. But he is very adept in the slot. And with Aqib Talib and Marcus Peters already on board, that’s probably where Robey-Coleman will play exclusively.

What it means: The Rams’ secondary has made a complete 180, from barren at the start of the offseason to quite possibly the NFL’s best before the start of the new league year. Their two starting corners, Peters and Talib, have combined for seven Pro Bowl appearances. Robey-Coleman was graded 19th among 121 corners by Pro Football Focus last season. Behind them are Kayvon Webster, Sam Shields, Troy Hill and Kevin Peterson, four solid depth pieces.

What’s the risk: The only real risk here is that it further cuts into the Rams’ cap room and keeps them from adding other players -- specifically, edge-rushers, run-stuffers, a center and, now that Sammy Watkins is gone, potentially a wide receiver. The Rams will be at roughly $30 million in cap space once they cut ties with wide receiver Tavon Austin. They can save an additional $3.5 million or so if they let go of Webster, who is recovering from a ruptured Achilles tendon.

Sam Shields, CB

The Rams signed cornerback Sam Shields on Thursday. The former Green Bay Packer has been a Pro Bowler but spent most of the past two years away from the NFL because of concussions. Here's a closer look at the signing:

Grade: B. This is a prototypical low-risk, high-reward signing. The Rams are buying low on Shields. If he gives them anything close to what he gave the Packers earlier in his career, it's a steal.

What it means: The meaning of this signing changed completely in a matter of hours. Shortly after adding Shields, the Rams acquired All-Pro cornerback Aqib Talib from the Denver Broncos for a 2018 fifth-round pick. Talib joins another shutdown corner in Marcus Peters on the outside, which means that Shields -- along with Kayvon Webster, who is recovering from a ruptured Achilles tendon -- will serve as depth. Shields can try to regain his form without the pressure of producing immediately.

What's the risk: The obvious risk is that concussions continue to keep Shields off the field. He hasn't played since suffering his latest concussion in the opener of the 2016 season, which was the fourth of his NFL career and his second in a span of nine months. The risks lie in Shields' long-term health, not necessarily the Rams' immediate plans. At his best, Shields was a speedy matchup corner who was able to compile 18 interceptions from 2010 to 2015. He can help make the Rams special at cornerback.