Jason Hatcher, who had 11 sacks last year, will be welcomed to a Redskins defense whose lineman registered a total of only 4.5 sacks last season. (Jonathan Newton/The Washington Post)

The Washington Redskins ratcheted up their free agent activity Thursday, agreeing to terms with Pro Bowl defensive lineman Jason Hatcher and three other players while hosting another veteran trio and lining up visits Friday with a handful of others.

In addition to Hatcher, who agreed to a four-year contract worth a reported $27.5 million, Washington found a prospective starter in inside linebacker Darryl Sharpton, formerly of the Houston Texans, and another starting candidate in cornerback Tracy Porter, who last played for Oakland.

Hatcher, however, is the biggest catch. At 6 feet 6 and 299 pounds, he led all NFL defensive tackles with 11 sacks last season. His arrival not only strengthens the Redskins’ pass rush, it also significantly weakens division rival Dallas, which also released DeMarcus Ware before he signed with Denver earlier this week.

Hatcher spent the first five seasons of his career as a backup before breaking into the starting lineup in 2011. He lined up at right defensive end in the Cowboys’ 3-4 formation before switching to defensive tackle when the Cowboys went with a 4-3 front this past season.

The Redskins entered the offseason with glaring needs on defense, particularly in their secondary and pass rushing. Washington re-signed rising defensive end Chris Baker earlier this month and used the franchise tag last week to retain outside linebacker Brian Orakpo. Then on Tuesday, the team re-signed inside linebacker Perry Riley.

But through the better part of three days, the team’s needs for additional pass-rush help and impact players in the secondary went unfilled. Washington instead acquired wide receiver Andre Roberts, guard Shawn Lauvao and linebacker-special teams ace Adam Hayward.

Hatcher had visited both the Seattle Seahawks and Oakland Raiders and was scheduled to visit Washington on Friday, but the Redskins pulled off a deal with him in advance of his trip to the area.

His acquisition was widely welcomed by Redskins players, who took to Twitter to welcome their former foe and expressed joy over the move in text messages.

Hatcher himself took to Twitter, stating, “I’m proud to say I will be joining the Redskins. God is good. Work time!!!!”

The move puts into question the Redskins’ plans for Stephen Bowen, who has started at right defensive end for the last three seasons. Bowen, a close friend of Hatcher’s and a teammate of his for five seasons with Dallas, is coming off microfracture surgery and will count for $7.02 million against the cap this season. But he could remain in the Redskins’ plans in some form. Defensive coordinator Jim Haslett likes rotating his linemen in and out of games to keep them fresh.

But Hatcher’s impact — if he can produce as he did in Dallas — will be welcomed to a unit whose linemen tallied only 4.5 sacks last season. Orakpo recorded 10 sacks, and fellow linebacker Ryan Kerrigan added 8.5. But Washington struggled to generate consistent pressure on quarterbacks, which in turn exposed weaknesses in a troubled secondary.

Redskins decision-makers believe Hatcher’s addition could help ease pressure on their defensive backs. But they still aim to add more talent to the secondary and began doing so Thursday with the addition of Porter.

Paired with leading cornerback DeAngelo Hall and second-year pro David Amerson, Porter’s versatility could help. A seven-year veteran and former second-round pick of the New Orleans Saints, Porter has the ability to play on the outside and also line up on the inside, covering slot receivers.

Washington does not appear to be finished addressing concerns in its secondary. The team was scheduled to host former Seattle Seahawks cornerbacks Brandon Browner and Walter Thurmond on Thursday evening and Friday, respectively. Former Cowboys linebacker/defensive end Anthony Spencer also visited Thursday, but it was unclear whether he was offered a contract.

In Sharpton, the Redskins acquired a potential starter alongside Riley, who is expected to take on a larger playmaking and leadership role with London Fletcher retired. Like Riley, Sharpton is entering his fifth NFL season. The Houston Texans selected him one pick before Washington drafted Riley in the fourth round in 2010. But unlike Riley, who has started the past 21 / 2 years, Sharpton has never served as a full-time starter. He recorded 87 tackles and one forced fumble in 2013, when he started eight of 15 games. The 5-foot-11, 235-pound Miami product had made 11 starts in 27 games from 2010 to 2012.

Strong safety and free safety remain as glaring needs. The team flirted with the top free agents at those positions but resisted the temptation to engage in a bidding war, and they signed elsewhere.

On Thursday, the team hosted former Steeler Ryan Clark, who also played in Washington in 2004 and 2005. Clark’s visit went well, according to his agent, but he left Redskins Park without having signed a contract. The two sides remain in discussions.

Washington’s final signing of the day was Clifton Geathers — a 6-8, 340-pound backup defensive end who last played for the Eagles. His uncle, Jumpy Geathers, played for Washington from 1990 to ’92.

The Redskins also are scheduled to host former Houston tight end Owen Daniels on Friday.