The San Francisco 49ers replaced Robert Saleh with Raheem Morris this offseason, but they did not merely exchange one defensive coordinator for another.

They changed academic departments.

“Raheem majors in the secondary, whereas Saleh majored more in linebacker play,” 49ers coach Kyle Shanahan said. “To be a good coordinator, you have to know all three levels, and they both do.”

Saleh is apparently the linebacker professor. Morris teaches defensive backs, with electives in five-man fronts, manufactured pressure and positions that sound like rejected Marvel characters.

Morris has imported two hybrid roles into San Francisco: the “star” and “fever backer.” The star is an every-down nickel defender who can cover the slot, support the run and rush the passer. The fever backer can line up off the ball, attack from the edge or drop into coverage.

The difference was visible during Tuesday’s joint practice with Saleh’s Tennessee Titans. Morris repeatedly sent Fred Warner after quarterback Cam Ward, a significant departure from Saleh’s traditionally low blitz rates. One disguised coverage also confused Ward into throwing a pick-six to safety Ji’Ayir Brown.

Linebackers coach K.J. Wright offered an explanation that clarified almost nothing.

“You’re off the ball, you’re on the ball, you get a fever, you’re sick,” Wright said. “It’s like you can do so many things. It’s a football sicko.”

Somewhere, a traditional depth chart quietly burst into flames.

The changes have impressed San Francisco’s players. Left tackle Trent Williams said “everything’s different,” while Brown called it his favorite training camp. Renardo Green said Morris’ defense allows him to play faster, and Deommodore Lenoir praised the coordinator for simplifying his responsibilities.

That does not necessarily mean Saleh made defensive backs complete a written exam before every snap. His 2025 scheme was compromised after Nick Bosa tore his ACL, Warner suffered a season-ending ankle injury and the 49ers finished last in sacks. Without pressure up front or their primary communicator, Saleh had to place more responsibility on the secondary.

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Morris now has Warner and Dre Greenlaw back, while using blitzes and simulated pressure to compensate for Bosa’s continued absence.

The new defense was also plenty physical against Tennessee. Three fights erupted within the first six snaps, and four players were reportedly ejected under the teams’ no-punch policy.

The reunion ultimately illustrated Shanahan’s distinction. Saleh returned with a linebacker-rooted system built on familiar principles. Morris countered with disguised coverages, aggressive pressure and defenders holding job titles that sound like medical conditions.

Both coaches want violence between the whistles and calm after them.

On Tuesday, their players mastered only half the lesson.