That has Mostert excited for the possibilities.
"That big guy, he came in here, and he's putting on a show," Mostert told reporters on Monday. "The way he moves and stuff like that, you can't teach that with any other O-lineman. He's definitely a difference-maker and a guy that we can definitely rely on."
Williams played three seasons for Kyle Shanahan when the 49ers head coach was the offensive coordinator in Washington.
"And he's been in this scheme before, so he understands what he needs to do to be great," Mostert noted.
Williams didn't play last season, but Shanahan's familiarity with the offensive lineman and Williams' reputation throughout his career was enough to entice the 49ers to target him as a replacement for the retired Joe Staley. Williams is a seven-time Pro Bowl selection and is known as one of the best at his position.
"His morale, his whole being right now is just fun, fun, fun," Mostert shared. "... He's been injured, and he's been out for some time and hasn't necessarily hit his stride. This year, he feels like he's definitely going to hit that, and we all see it. It is definitely something to witness."
Williams' excitement to get back on the football field, this time with a team that can compete for a championship, has been evident all offseason. He always has a smile on his face while discussing Shanahan's offense or his new teammates.
"Having football back in my life is reinvigorating," Williams said last month "... Coming out here with a team where we're all like-minded, we're all pros, everybody working their tail off day in and day out, it demands me to be a better player. I feel the pressure to be that Trent Williams of old, where I can step in and help this team."
Monday wasn't the first time Mostert has discussed Williams' athleticism. He did so last month, as well.
"Trent is definitely one of the most athletic O-linemen I've ever seen," Mostert said on August 27. "Just the way he moves out there. He gets to his blocks quick, and he makes our decisions, cutting and stuff like that, easier. Like I said, it's truly a blessing having him out there."
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