After all, it had been a long time since Foster was able to play football in pads at full speed. He made sure not to take it for granted.
"It was just a thrill to finally put some pads on," Foster said. "Finally."
For Foster, it had been 202 days since he last put on pads and played. That was for Alabama in the College Football Playoff National Championship, a disappointing last-second loss to Clemson. Considering all that has happened in the time since, it's no wonder that Foster was looking forward to getting back to business.
From the time the college season ended to Sunday's practice, Foster had surgery to repair a torn labrum in his right shoulder in February, attended the NFL scouting combine -- where he was sent home early for arguing with a hospital worker during player physicals -- and tested positive on a drug test for a diluted urine sample. All of that happened before the NFL draft, leading to a precipitous drop in the first round stemming from concern over his shoulder and the positive test.
After multiple attempts to get back into the first round, the 49ers traded up from early in the second round to No. 31 in a deal with the Seattle Seahawks. They stopped Foster's slide there, but new general manager John Lynch and coach Kyle Shanahan found themselves facing repeated questions about Foster's health and his ability to avoid trouble off the field.
Although the Niners said all along they expected Foster to be cleared and ready to go by training camp, reports continued to surface that perhaps his shoulder surgery didn't take and he would need to have a second operation. The 49ers stuck by the diagnosis of their doctors and trainers, all of whom believed Foster was on track to return.
"I heard all the same stuff and everyone was like, 'Aren't you worried he’s going to get hurt?'" Shanahan said. "I was proud of our doctors for putting themselves out there and giving their honest opinions of what they felt. And they feel it is healed and it's going to be good. I respect them for doing that because they went against the norm on that and that's not always easy. But I think worst-case scenario, what if he does come back and gets hit and hurts his shoulder again? What made me excited was I thought we acquired him the right way, the way we got him.
"If he does come back and his shoulder is hurt, we'd have to do re-surgery and it might hurt him in his first year. But we're also talking a shoulder and not a knee. That would be disappointing not having him the first year, but that's not something that I feel would affect his playing career."
The Niners mostly held Foster out of organized team activities, limiting him to non-contact drills and putting him through his paces in the classroom. The hardest part was keeping the excitable Foster from talking them into letting him play right away and keeping an eye on him to prevent him from jumping into a drill he wasn't supposed to be in.
"They were watching me 24/7," Foster said. "Sometimes I wanted to sneak out there and do a little warm up, a little drill, but at the same time I have got to do what's best for me and they know that as well."
Foster wasn't kidding when he said he had to be monitored.
"We told you about how we almost had to have a leash on him to keep him out of drills and all of that," Lynch said. "We've said, and you guys see us, we start smiling when we talk about the guy because there's so much to like about him and I think we've only grown to appreciate that more since he's been in the building. He's got an excitement that's infectious.
"He's an alpha dog, he wants to lead. He's ready, he's eager and we are certainly excited to watch him play."
In an effort to be ready mentally when he finally could play again, Foster spent extra time with linebackers coach Johnny Holland and assistant DeMeco Ryans. Shanahan came away impressed with how Foster was able to stay engaged in meetings even without the reward of getting to translate what he learned in the classroom to the field right away.
Even after his teammates left for summer break, Foster stayed behind in Santa Clara and spent most of his time at the team facility continuing to rehab so he'd be ready to go at the start of training camp.
As it turned out, that's exactly what happened, as Foster got his clearance to return last Wednesday. He entered camp with no restrictions and nothing changed when the 49ers put the pads on Sunday.
In his first three practices, Foster has worked exclusively at weakside linebacker on the third-string defense. Like most rookies, he'll have to earn his promotions up the depth chart, but that process is already underway as Foster has impressed with his instincts (he has two interceptions in his first three practices) and his willingness to learn. If he continues to make plays, he's expected to push veteran Malcolm Smith for the starting job.
"From what I've seen, he understands the game," middle linebacker NaVorro Bowman said. "We got the chance to work out together several times and he's excited to be around me, so I think that's the first step to building a relationship the way that we're trying to get to. We've seen what he's done in college. We just want to transfer it here to the NFL and he's open ears, open to learning new things and that's what we're going to need to get to that point. I really do think he'll have a successful career."
Bowman has already begun taking Foster under his wing, teaching him some of the details such as how to take better pursuit angles because the speed and cutting ability of players in the NFL is much greater than it was in college.
And, as Lynch was quick to point out, Foster also has the type of attitude that can help keep teammates fired up.
"Reub is nice. He's a dog, too," cornerback Rashard Robinson said. "I remember playing against him in college. He's always been that type of player. He's a type of guy like me. He likes to hit, run around and talk trash, so it's going to be fun."
As for the shoulder, Foster said Sunday he isn't tentative at all during practices and doesn't even think about it when he's playing. In fact, if Foster had any nerves at all in his first padded NFL practice, it was a result of seeing how big and strong Bowman looked when dressed out.
"I was worried at first," Foster said, laughing. "You look at Bow and then you look at me, he's a man. That's a man. You see his arms? And it's the NFL -- there are a lot of grown men, it's not college. At first I was worried and anxious and nervous."
But those butterflies quickly went away with the first thud of the pads. For the first time in nearly seven months, Foster is back to football.