Head coach Kyle Shanahan desperately wanted the 49ers to draft Joe Williams.
And it’s now becoming a bit clearer why he lobbied so hard for the Utah running back.
After a slow start to training camp, the fourth-round pick has run more authoritatively in recent practices. He said his decisiveness is partly due a better grasp of the offense and a recent conversation with running backs coach Bobby Turner.
“I saw it myself,” Williams said of his slow start to camp, “and coach Bobby T had talked to me. … I told him ‘Just keep coaching me. Just keep staying on me.’”
Said Shanahan: “I thought he had his best day (Thursday) and then it seemed like today was better than that. It takes time with some of these guys, by no means has he arrived with two good practices.”
Williams ran the second-fastest 40-yard dash among running backs at the combine and ended his college career by averaging 190.2 rushing yards and 7.1 yards per carry in his final seven games.
Still, general manager John Lynch didn’t have Williams on his draft board due to off-the-field concerns before Shanahan and Turner convinced him to reconsider.
Williams acknowledged he arrived for the offseason program out of shape, but his fitness is no longer an issue. He stayed in Santa Clara to train during the five-week break before camp.
“I thought I was in shape just because I was doing a lot of stuff for the combine and pro day,” Williams said. “But being out here with guys who have spent eight, nine, 10 years in the league and really have their bodies in shape – I wasn’t there yet.”
Debut delayed: Wide receiver Louis Murphy, 30, has yet to practice with team after signing Monday.
Murphy, who hasn’t played in the NFL since he tore his ACL with the Buccaneers in October 2015, is working himself into shape and will make his practice debut next week.
“He did a real good job in his workout, but we worked him pretty hard and we could just tell he hadn’t been around football for a little bit,” Shanahan said. “So we don’t want to throw him out in the fire and risk him getting hurt right away.”
New home: A day after the 49ers parted with Bruce Ellington, the wide receiver was claimed off the waivers by the Jets.
Ellington will reunite with Jets offensive coordinator John Morton, who was his position coach during his rookie season with the 49ers in 2014.
Familiar name: Linebacker Aaron Lynch was excused from practice after his wife gave birth to their second child. The baby’s name: Samson John Lynch.
Injury report: Defensive tackle DeForest Buckner (ankle), tight end George Kittle (hamstring), safety Jaquiski Tartt (rib), center JP Flynn (knee), cornerbacks Keith Reaser (knee) and Zach Franklin (ankle) and linebackers Eli Harold (concussion), Brock Coyle (rib) and Donavin Newsom (neck) were sidelined.
Rookie linebacker Reuben Foster went down with an ankle injury in practice and spent a few minutes on the field. He walked off without assistance and returned after missing one snap.
Eric Branch is a San Francisco Chronicle staff writer. Email: EBranch@sfchronicle.com Twitter: @Eric_Branch