Ahkello Witherspoon was criticized for his finesse tackling in college, but the 49ers rookie cornerback stood his ground when running back Carlos Hyde sprinted toward him near the end of practice Wednesday.
And that turned out to be a mistake.
The 228-pound Hyde, who outweighs Witherspoon by more than 30 pounds, capped a six-yard touchdown run by bulldozing the third-round pick at the goal line.
Witherspoon likely expected Hyde to give him a bump in the no-tackling session, but instead he lowered his shoulder and sent Witherspoon sprawling.
Welcome to the NFL.
After Witherspoon received the rag-doll treatment, defensive coordinator Robert Saleh said he was caught flat-footed and expressed confidence in his tackling ability.
“I’m not worried about that last play,” Saleh said. “They’re not tackling drills, and that caught him off guard. We’ll see when we’re actually allowed to tackle and I have full faith that Ahkello’s going to do exactly what he’s been coached to do. He’s not a coward by any means. He will get in there. He will tackle.”
The lanky Witherspoon, 6-foot-3 and 195 pounds, has been viewed as a candidate to earn the starting spot opposite Rashard Robinson. He’s been playing with the second-team defense early in training camp while Dontae Johnson and Keith Reaser, who was recently sidelined by a knee injury, have shared first-team snaps.
Wait, rookie: First-round pick Reuben Foster has three interceptions in five training-camp practices, but he’s still working primarily with the third-team defense.
Saleh was asked when Foster will be promoted to the second-string.
“Reuben, he has a lot of flash plays,” Saleh said. “The best way I can explain with Reuben is he’ll get his opportunity when he absolutely, absolutely deserves it.”
Foster’s aggressiveness is among his strengths, but it’s also a reason why he’s been beaten in pass coverage during camp.
Injury report: In team drills, defensive tackle DeForest Buckner walked off slowly and later had his lower left ankle heavily taped during practice. He did not return and was replaced on the first-team defense by rookie Solomon Thomas and Chris Jones.
In other injury news, undrafted rookie cornerback Zach Franklin (left leg) was injured during individual drills and walked slowly off the field with a trainer.
Safety Eric Reid (ankle) only participated in individual drills and appeared to be running at full speed. Linebacker Eli Harold (head), tight end George Kittle (hamstring), safety Jaquiski Tartt (rib), safety Jimmie Ward (hamstring), center JP Flynn and Reaser did not practice. Kittle took part in individual drills.
Eric Branch is a San Francisco Chronicle staff writer. Email: EBranch@sfchronicle.com Twitter: @Eric_Branch