He was surprised to see one of his teammates working on the practice field. Wide receiver Sammy Watkins was running pass routes.
"I caught him doing some extra work, so I know he's a hard worker," Nelson said.
The Chiefs were impressed by Watkins' speed and big-play ability during recently concluded offseason practice, but they knew he had those qualities. Those qualities are why in March they gave him a three-year contract worth $48 million.
The Chiefs have been, to some extent, caught off guard by how badly Watkins wants success, how much he wants to make good on his contract, how much he wants to be another strong receiving option in an offense that already features two top skill players in tight end Travis Kelce and wide receiver Tyreek Hill.
They're asking him to learn all of their wide receiving positions, and he hasn't flinched.
"We're moving him all over the place, and he's handled it," coach Andy Reid said. "We've overloaded him with that. That's how we do it in this offense. That's something new for him. You can tell he's a guy that takes it away from here and studies. When we're doing all these different formations, you've got to do that. You just can't get it all when you're here. You've got to go back and you've got to review, and he's done that and he's really limited the mistakes for all we've given him."
Watkins, drafted fourth overall by the Buffalo Bills in 2014, hasn't been a bust in his four NFL seasons, but neither has he completely delivered on his immense potential. He did have nine touchdowns and more than 1,000 receiving yards for the Bills in 2015.
Playing with Kelce and Hill, Watkins may not get the opportunity to post big numbers this season. But with Patrick Mahomes at quarterback, the Chiefs may be prolific enough on offense that all of their top receivers will thrive.
Being able to play all of the wide receiving positions and line up in a variety of places in a formation should help Watkins be productive.
"This offense is the broadest offense I've ever been in," Watkins said. "It's definitely a mental challenge. But I think that's what kind of gets me up every day to study the plays and come out here encouraged. Anybody can get the ball and I've got to learn all the positions. I can't just learn one position. I have to be focused and tuned in, in meetings. You have to do that off-the-field work and stay in your [playbook].
"You just get more opportunities on linebackers [and] safeties. It's definitely easier working against a linebacker or getting open against safeties."
Watkins has played for Reid for about three months, but he said the coach is already making him a better player. Part of that is Reid's insistence that Watkins learn all of the positions.
"He's a full-speed guy," Watkins said. "Every day you come out here, every rep, it's full speed. That's just going to help me translate that during the game. He's helped me in this short amount of time with just being a compete receiver, not just being [a receiver who just runs go-routes]. I've got to learn the whole route tree. The standard that he wants ... he's called me out in meetings. That's what you want as a player. I take full advantage of all those things.
"I've never been in an offense like this, around a coach that just feels like he's obsessed with the game and makes you want to be obsessed with it, too, to know more about the offense. The more you break it down the more you can be available and switching different positions."
Watkins called this year's set of offseason practices the best of his career. That's not always an accurate predictor of regular-season success. But Watkins has made some spectacular catches, including a number with only one hand.
"He made some catches sometimes that I don't know how they're possible," Mahomes said.
Watkins is only beginning the Chiefs portion of his career, but he's off to an encouraging start.
"I've been my best this year with just getting in shape and learning the offense," Watkins said. "I just can't wait until I fully get engaged into the plays and get in shape. I feel like once I do that I can be a better player for the team."