SANTA CLARA — It started in August during the 49ers' joint practices in training camp, when few members of the Denver Broncos coaching staff pointed out the brash and aggressive personality of No. 54.

At the time, no one suspected that the player stirring up frustration on the opposing sidelines was Fred Warner, who had worn No. 48 during his rookie year. This no longer was the calm, calculating BYU product whose nickname in the 49ers locker room was “The President.”

Something had changed -- like a switch had been flipped. The impetus for that change was the addition of fellow linebacker Kwon Alexander to the roster.

Alexander’s season seemed to be over after he tore his pectoral muscle on Oct. 31 in Arizona. But after the 49ers clinched the No. 1 seed in the NFC and earned a first-round bye, Alexander's return has become a serious possibility. On Tuesday, the 49ers medical staff cleared him to play before the 49ers-Vikings divisional round clash.

Throughout his rehab, Alexander has remained close to the team. His presence is a valuable spark that keeps the fire burning on the defense. Nick Bosa even referred to the linebacker as the MVP of the team because of what his energy and attitude brings to the table.

When Alexander speaks to the media, however, he always is smiling and polite while fitting in the word "legendary" as many times as he can in his replies. It is a stark contrast to how his teammates describe him when the game clock starts.

“That mentality change when you go on the field,” Alexander said last week. “Ain’t no more nice guys, nothing like that. It’s just straight competition. We like to get the job done, so that’s what we’re trying to do. We’re going to work every day to get it done, that big goal.

“I’ve been like this since I was young. I’ve always been a competitor. I always like to work hard. I always like to outwork people. I always like to beat people too, so it’s been from the start for me, just being happy and just going out there and work hard.”

Alexander also uses the football field as his release. Any of the aggravation and frustration of the day gets taken out on whoever is on the other side of the field.

“That’s the thing about playing football,” Alexander said. “A lot of people go though a lot of things in life and need to be able to let it out. Some people got a lot of stuff built up. So once we are able to go out there and do what it is, we just let everything out.

“You can be angry at whoever you want. Whatever made you mad, point at them. You know what I’m saying? Point at the opponent and take it out on them. That’s what we’re doing. We’re just having fun doing it.”

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Alexander recognizes that the 49ers' opponents will have a similar mindset, which is why he focuses on getting his teammates to push through just a little bit more. Even when he’s not on the field, his energy is evident on the sidelines.

“You got to flip that switch real fast and get to that confidence, that cockiness on the field cause you got to have that.” Alexander said. “Once you go against someone else they are going to have that same thing.

“You got to be able to beat theirs. That’s what we all have. That’s why I really love the team. They like to have fun. They have the confidence, swagger enough to do it and we’re going to do it.”