With the pads back on, the Detroit Lions picked up a slew of injuries in Monday's night practice.

Lions running back Jahmyr Gibbs did not finish practice after picking up a leg injury, according to the team. The Lions also said first-round rookie Terrion Arnold left early with an upper-body injury and second-round pick Ennis Rakestraw Jr. picked up an ankle injury.

Arnold left the practice after a one-on-one rep against Amon-Ra St. Brown, then Rakestraw left at the beginning of team drills with a slight limp.

WHAT WE KNOW: Detroit Lions RB Jahmyr Gibbs reportedly leaves practice with hamstring injury

Alim McNeill, Malcolm Rodriguez, James Houston, Kevin Zeitler and Sam LaPorta were all out of practice for the second day in a row. Gibbs went through position drills with both the running backs and wide receivers before he left during team drills. ESPN's Adam Schefter reported after practice that Gibbs sustained a hamstring injury.

Here are some non-injury observations from Monday's practice.

David Montgomery thrives as main RB

Brian Branch did not have a fun time trying to take down David Montgomery, who handled the bulk of the first-team load with Gibbs out and Craig Reynolds taking some snaps. Montgomery bowled through Branch during the one-on-one tackling drills, then followed that up by running him over during the goal line drills a few minutes later.

Montgomery had a pair of touchdowns during the goal-line portion by lowering his shoulder through a defender. Later in the game sessions starting at the 25-yard line, he followed a perfect pulling double-team duo of Graham Glasgow and Frank Ragnow for a walk-in touchdown from over 20 yards.

Zonovan Knight and Reynolds also had a pair of nice runs during the late-game 11-on-11 drills at the end of practice, showing burst to the second level and making one defender miss.

Campbell asks for more from WR depth, Vildor has nice day

The Lions have plenty of options jostling for snaps at wide receiver behind the solidified options up top, even with Antoine Green being waived earlier Monday. Before practice, Campbell said he's been impressed with some of Donovan Peoples-Jones' work in practice since the first preseason game, but overall wants to see more for from the receiving corps.

"We are waiting for any of those guys to step forward," Campbell said before practice.

Kalif Raymond was the main standout Monday behind the top two, showing his skills as a gadget guy on reverses and as a route runner out of the slot. Peoples-Jones, Daurice Fountain and Maurice Alexander all got work with the first team, plus plenty of two tight end looks featuring two of Brock Wright, Shane Zylstra and James Mitchell with LaPorta out.

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In the closing red zone drill, the Jared Goff tried to attack Kindle Vildor twice in the back of the end zone but both fell incomplete. On the first, Vildor jammed Williams off the line out of the slot, forcing a pass behind target since it was off time. On the following play, Fountain didn't cleanly secure a toe-tap catch, giving Vildor a chance to bat it free for an incompletion.

On the final play of practice, Aidan Hutchinson blew past Taylor Decker on the left side to sack Jared Goff on a fourth down from the five after Vildor's deflections, giving the defense a win to finish the day.

Trying to figure out kickoffs

The Lions are still trying to figure out how to exploit the new kickoff rules.

They ran it full speed on Monday night. Not live. But full speed.

On Sunday, Campbell and Lions special teams coach Dave Fipp watched every kickoff in the NFL in the first week of preseason games.

“Every time you see one, you learn something new,” Campbell said. “The team's doing this, they're not doing this, and you learn it on both sides of the ball.”

In Campbell’s mind, it comes down to risk and reward.

The risk of giving up a huge play versus the reward of pinning a team inside the 25.

“That's the battle that we're going back and forth with as we continue to rep it,” Campbell said.

Sione Vaki improving on two sides of ball

Sione Vaki remains one of the most intriguing players in camp.

Vaki was one of the deep returners on kickoffs with Kalif Raymond on Tuesday night.

On one return, he became a blocker.

On another, he had a nice return up the sideline.

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“Certainly, on special teams, we feel growth,” Campbell said. “So there is improvement.”

The Lions drafted Vaki as a running back, and he had four carries for 29 yards against the New York Giants. “He's growing,” Campbell said. “I think what, what you got to remember is he has not played the running back position. He's still so relatively new to it.”

Vaki is still learning how to run inside, but he’s shown flashes on the perimeter.

“A lot of it is, man, your landmarks in the run game, inside runs, tackle to tackle, vision inside, the feel of it,” Campbell said. “He just needs a lot of reps at that. The perimeter stuff? He's got to feel. He's growing in protection. He's starting to figure it out.”

If Vaki can play running back it will be a bonus.

His main contribution is expected to be on special teams.

“Here's what you like,” Campbell said. “He's got a skill set, you know, he's a very good athlete, and he did play some defense in college. Played a lot before his running back. And so you really feel like, 'Okay, this kid can help you on special teams.' And then, 'All right, as he's growing at running back, are there other things maybe we can do with him down the road, you know, on offense? Can we package him a little bit?' We'll see.”

D-line does well in 1-on-1s

Hutchinson had another great day, including a clean win against Penei Sewell to begin the one-on-ones in the trenches, using a rip to the inside to win with a blend of speed and power. Defensive tackle Brodric Martin had a clean win against Frank Ragnow, prompting Ragnow to line up again against defensive tackle Kyle Peko, who also won with speed against the All-Pro center.

"I'm lucky to go against a guy like (Ragnow)," Peko, who signed with the Lions in the offseason, said. "He's getting my skills in line for the season."

After the slow start by the offensive line, the starters finished the one-on-ones with four straight wins against various members of the defensive line.

This article originally appeared on Detroit Free Press: Detroit Lions training camp observations: Injuries starting to pile up