ALLEN PARK, Mich. -- Some thoughts, observations and analysis after the second open practice of Detroit Lions training camp Monday.

1. Darren Fells had a good day: With Eric Ebron sitting out due to a hamstring injury, the Lions looked a lot to the offseason free-agent signing from Arizona to play with the No. 1 unit as both a blocker and a receiver. Already one of the better blocking tight ends in the league, Fells showed he has some hands Monday.

His best catch came over the middle from Matthew Stafford, where he grabbed the ball in front of safety Tavon Wilson and progressed down the field. Unfortunately for the Lions, Wilson ended up injured on the play and missed the rest of practice.

But Fells is a player who could be a legitimate red-zone threat and a very tall target for Stafford -- think Joseph Fauria with better blocking ability -- and that's important considering Ebron hasn't played a full 16 games in a season in his career.

"They want me to come in and be a big-time blocker, so I'm planning on doing that," Fells said. "If they want me to go out and run routes, I'll go do that, too."

The Lions likely won't ask that much of him in route-running once Ebron returns, but the fact that he is showing he has those skills gives Detroit a good No. 2 option behind Ebron. That could be beneficial, because the Lions could have the depth to run more two-tight end sets in 2017. Lions coach Jim Caldwell said that's always been part of the team's offense. Don't be surprised if it is featured more this season, especially with the fullback disappearing from the offense.

Defensive end Cornelius Washington went down Monday with what looked to be a left leg injury and did not return to practice. Steven King/Icon Sportswire

2. Defensive line depth is a concern: I wrote about it Sunday, but the Lions have to be worried about their depth -- particularly at defensive end. Potential starter Cornelius Washington went down Monday with what looked to be a left leg injury and did not return to practice. Caldwell didn’t have an update on Washington's status, but acknowledged that depth can be a fickle thing in the league.

The Lions are down four defensive ends at present with Ezekiel Ansah, Armonty Bryant and Jeremiah Valoaga on the PUP list and Washington's injury. That leaves Detroit with five healthy defensive ends and one of them, Brandon Copeland, has been spending time trying to win the SAM linebacker job, too. At some point, Detroit might want to look for another defensive end or two, just to give some cover during camp.

3. What's up at left tackle: The man protecting Stafford's blind side most of Monday? It wasn't a former first-round draft pick (Taylor Decker, Greg Robinson) or a player who was even drafted (Cyrus Kouandjio, Corey Robinson).

Nope, it was undrafted rookie Storm Norton out of Toledo. Don't read too much into it yet -- all four of the players above him on the likely depth chart are either on injured lists or recovering from injury -- but that Norton would be plugged in as the team's left tackle shows he's made progress as a potential roster sleeper.

It's even more surprising considering the Lions also have Cornelius Lucas, who has more experience, not playing left tackle in that situation. It also might signal how Detroit feels about Lucas as a left tackle at this point. At some point soon, particularly since they were taken off injury lists, Greg Robinson and Kouandjio should be competing for the starting job. But until that happens, Norton might continue to be a deep sleeper candidate for a roster spot -- or at least a practice squad job.

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4. Mixed rookie reviews: Receiver Kenny Golladay had another pretty good day, snagging a couple of passes in team drills and making a nice jumping catch over Johnson Bademosi in one-on-one receiver-cornerback drills. He's continuing his progress.

Fourth-round pick Michael Roberts was not as fortunate, though. He received more work with Ebron missing practice and it didn't go well. He had one clear drop and was also stripped by Wilson on another reception, losing the fumble. He should win the No. 3 tight end job -- and it's still very, very early in camp -- but drops and fumbles are not going to fly for long with a pretty veteran offensive group.

5. Golden Tate's chemistry: The receiver had the play of the day at practice, catching a deep route from Stafford during an 11-on-11 period and getting his feet in-bounds before heading out of bounds and falling toward the VIP area. It was the type of catch the Lions are used to Tate making and one that comes through advanced work between quarterback and receiver through the years. Stafford and Tate are comfortable with each other, and that play showed it.

This and that: Bruce Gaston has missed the first two practices of camp due to a death in the family. ... The punt returner battle continues with the same general candidates -- Tate, Jamal Agnew, TJ Jones, Jared Abbrederis and Keshawn Martin. That Tate continues to line up there is intriguing, but ultimately the job should go to someone else. ... Nick Bellore, Ebron and Gaston were the only Lions to miss practice Monday, although Theo Riddick remained in his red no-contact jersey. ... Former Indiana basketball coach Tom Crean was a guest at Lions practice, spending most of his time chatting with general manager Bob Quinn. Lions coach Jim Caldwell said he knew Crean in passing when he was with the Colts because he would sometimes come to practice with former Colts president Bill Polian.