The move pushed Jason Pinnock, who had started the first five games of 2025, to the sidelines. Pinnock did not play a single defensive snap against Tampa Bay, appearing only twice on special teams.
On a Monday conference call with reporters, head coach Kyle Shanahan explained the decision and outlined the 49ers' plan to gradually reintroduce Mustapha into a full-time starting role.
"He (Pinnock) was the starting safety for the first five weeks," Shanahan said. "We thought Ji'Ayir Brown had been earning some time at safety, and we knew with Mustapha coming back, we were going to start rotating and getting Mustapha in there so he could eventually take that over.
"We know Mustapha is going to be one of the starters out there. It was nothing against Jason. We just knew we had to make a decision to rotate one of those guys with Mustapha, and we went with rotating Mustapha and Sigle, which gave really that week to give Tig (Brown) his opportunity to play a whole game at safety."
Shanahan shared that Brown had earned an opportunity to show what he could do in the starting lineup. Sunday marked only his second start of the season. However, in previous games, he has taken on a hybrid linebacker role when the 49ers needed extra help on the field.
The 49ers envisioned Pinnock contributing in that "big-nickel" role, but the flow of the game against Tampa Bay prevented that opportunity.
Shanahan shared that Brown did a "decent job" against the Buccaneers, adding, "I thought he was physical. I thought he made some plays, not too many mistakes. I thought Tig was solid."
As for Mustapha, Shanahan was encouraged by his performance in the 21 defensive snaps he played.
"I think he got about 20 plays, and he looked good and moved around, flew around," Shanahan noted. "He was ready for that moment, and I liked that we were able to get him in there, do all that stuff, and get him out healthy. Hopefully it'll be closer to that this week."
Shanahan also made it clear that the starting safety spot next to Mustapha is still up for grabs as the 49ers head into Week 7 of the 2025 NFL season.
"I think we've got three guys who are capable there, and those are what all those three guys are battling for," Shanahan said. "I don't think one guy's fully taken it and run with it like Mustapha did last year. So, that's something that we're going to continue to evaluate. But I don't think any of that's set in stone. We're trying to hope that they make that decision for us."
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