SANTA CLARA Mike McGlinchey Jersey , Calif. (AP) — The San Francisco 49ers agreed Monday to sign free-agent linebacker Kwon Alexander to a four-year contract worth $54 million.The two sides reached a deal quickly after teams were allowed to contact pending unrestricted free agents, a person familiar with the contract said. The person spoke on condition of anonymity because the deal can’t be finalized until the new league year starts Wednesday.Alexander entered the league as a fourth-round pick by Tampa Bay in 2015 and made the Pro Bowl his third season as a replacement for an injured player. But he tore the ACL in his left knee last October and played just six games. That didn’t stop San Francisco from rewarding him with the richest deal ever for an inside linebacker to pair him with 2018 third-round pick Fred Warner.The 49ers paid a steep price at linebacker just two years after using a first-round pick on Reuben Foster. Foster had a series of off-field problems and was released last November after being accused of domestic violence against a woman at the team hotel the night before playing Tampa Bay.Prosecutors ultimately decided not to pursue charges but the 49ers had already cut ties with Foster, who also was accused last offseason of domestic violence before that case was dropped when a judge ruled there wasn’t enough evidence after the accuser recanted her allegations.Alexander will be added to a defense that set an NFL record for futility with just seven takeaways, including a record-low two interceptions. As an inside linebacker, Alexander is not known as a playmaker but he does have six career interceptions, six forced fumbles, two fumble recoveries and seven sacks in 46 games.Alexander’s most productive season came in 2016 when he led the NFL with 108 solo tackles and also had 12 tackles for loss. He has averaged 8.3 total tackles per game in his career, the sixth most in the league since 2015 among players with at least 25 games played. But Alexander also led the NFL with 67 missed tackles from 2015-17, according to SportRadar.Alexander has missed 14 games with injuries the past two seasons and also was suspended for four games as a rookie for violating the NFL’s policy on performance-enhancing substances. The San Francisco 49ers are officially into the offseason following a 2018 season that did not meet expectations. The team entered with hopes of contending for a playoff appearance, but stumbled to a 4-12 record after losing quarterback Jimmy Garoppolo to a torn ACL in Week 3.Expectations will climb again in 2019, but before we get into that, it’s time to take a look back at the season that was for the current roster. There will be turnover in the coming months, but let’s start the offseason with a stock report on the 49ers roster. We’ll go through each position group and offer stock up or stock down for each player, and then stock up or stock down for the position group as a whole. Today we move on to the cornerbacks.Richard Sherman: Stock up2018 was Sherman’s first season without an interception. The lack of turnovers isn’t indicative of the veteran cornerback’s performance this season though, who was his typical lock-down self on the left side of the 49ers’ defense. Sherman totaled 37 tackles, three tackles for loss, one sack and four pass breakups in 2018. He allowed just 0.72 yards per coverage snap per Pro Football Focus, the fifth-lowest total among qualifying cornerbacks. Sherman’s play on the field and presence in the locker room has been worth every penny of his three-year, $39-million contract so far. Sherman offers the 49ers stability on an otherwise rotating secondary of young, inexperienced players.Ahkello Witherspoon: Stock downWitherspoon’s encouraging finish last season didn’t carry over to 2018. The second-year starter struggled with the added attention opposite Sherman, giving up six touchdowns in his first six games. His 44.9 grade from Pro Football Focus ranked Witherspoon 116th among all NFL cornerbacks. After a couple games on the bench, Witherspoon returned to action but suffered a season-ending knee sprain against the Seahawks in Week 15. He’ll go into the 49ers’ offseason program in competition for a starting role with rookie Tarvarius Moore.K’Waun Williams: Stock slightly downWilliams was reliable in 2018, if nothing else. He started 11 games throughout the season and played in 14. The 49ers’ nickel cornerback totaled 45 tackles, 3 tackles for loss and two pass breakups this season. Williams merited a 66.7 “Above Average” grade from PFF Roger Craig Jersey , only good for 59th among qualifying cornerbacks. D.J. Reed is the only reason Williams’ stock is down at all. The rookie replaced Williams in Weeks 14 and 15, performed well, and seems primed to compete with the veteran for the starting role in 2019.D.J. Reed Jr.: Stock upReed spent time at both nickel cornerback and free safety throughout the season. His best game came at nickel though, racking up a team-high 12 tackles, three tackles for loss and a sack against the Denver Broncos in Week 14. Despite only starting two games, Reed still managed 41 total tackles, three tackles for loss, one sack, one quarterback hit and a forced fumble. The 49ers’ fifth-round pick in 2018 showed a valuable versatility throughout the season and the ability to challenge Williams for the starting nickel role in 2019.Tarvarius Moore: Stock upWitherspoon’s knee injury against the Seahawks gave Moore a short audition to close out the season. The 49ers’ third-round rookie held his own when on the field, totaling 23 tackles, two pass breakups and a forced fumble against the Chicago Bears in Week 16. Shanahan praised Moore after the season, making it known that he’d be in completion with Witherspoon for the starting role opposite Sherman in 2019. Greg Mabin: Stock unchangedMabin made the 49ers’ 53-man roster to start the season and spent the first eight weeks on the active roster. He was waived in Week 9 and after a short stint on the practice squad, Mabin returned to the 49ers’ roster in Week 10. He worked his way into the cornerback rotation early in the season but only managed 16 tackles, one pass breakup and a forced fumble. Mabin played on a one-year contract and is an exclusive rights free agent this offseason.Emmanuel Moseley: Stock upMoseley was promoted to the 53-man roster before the 49ers’ Week 9 win over the Oakland Raiders. He dislocated his shoulder early in the game and required season-ending surgery. Prior to his promotion, Moseley was the 49ers’ highest-paid player on the practice squad, indicating he’d received interest from other teams. Moseley, signed as an undrafted free agent in 2018, is contracted through the next season, and will have an opportunity to complete for a more prominent role in 2019.Overall: Stock slightly downThe left side of the 49ers’ defense is set with Sherman in 2019. Williams and Reed, if he isn’t pulled in the safety scene, should be in competition for the starting nickel cornerback spot. The weakness resides opposite Sherman at right cornerback, where Witherspoon and Moore will battle for the starting spot in the offseason. Neither has proven capable of handling the role, and the 49ers may add more competition through free agency or the draft.