It's customary during the first week of the preseason and whenever NFL teams conduct joint practices for officiating crews to take part in training camp sessions. Their role is to assist the teams with how that season's rule changes will manifest themselves on the football field.

They do this by talking to players and coaches individually and in groups during practice, meeting with them afterward as a whole team to discuss the changes in more detail, and treating the 11-on-11 periods of practice like games, complete with yellow flags being tossed whenever an infraction occurs.

The referees' presence at practice also serves a beneficial purpose for the officiating crews themselves. After all, it's preseason for them, too, and as part-time employees of the league, they need time to get accustomed to the changes that were approved by NFL decision makers during the offseason.

For Jaguars-Patriots joint sessions this week, long-time NFL referee Pete Morelli and his 7-man crew (including a replay official) have been incorporated into the practices and will call the preseason opener between the two teams Thursday night at Gillette Stadium.

"For us, it's the first time we get on the field and see the players in live action," Morelli said after Tuesday's workout. "It helps our eyes kind of adjust to the game and the things they do. It helps all of us prepare for the game. Being officials, having four preseason games is the best thing in the world because we have the opportunity to work our way into a regular season game, to be ready to go in Week 1.

"And as the new rules come, they're like reactions to something that happened. We focus in on it, we talk about the plays and different aspects we want to work on. So, all this is helpful for us as officials."

Among the notable changes for 2017: launching is no longer allowed, meaning players cannot leave their feet and lead with the crown of their helmets to make a tackle or break up a pass; all crack-back blocks by eligible receivers are illegal within five yards of the line of scrimmage; more flexibility is being given to player celebrations, particularly after scores.  

"We used to need a Rolodex to figure out what they could and could not do [to celebrate]," Morelli remarked. "Now it seems… pretty much simple. We're going to have to see what happens out there. It'll be interesting, especially after the first [regular season] game. We don't anticipate too much in preseason."

In addition, the final decision on all in-game replay reviews will be made by the officiating department at league headquarters in New York City. Referees like Morelli no longer will retreat under a hooded replay machine on the sideline to watch the replays. A league representative will deliver a digital tablet to the referee on the field, halfway between the numbers and the hash marks, according to Morelli, so he can watch the replays in conjunction with the New York office.

"There'll be two sets on each 20-yard line. I'll go to wherever the nearest one is," he explained. "I think it'll be smoother, and the pace of the game will improve. As a matter of fact, we don't even have to wait until TV [comes back from commercial breaks] to make our announcement. We can make our announcement to the stadium immediately, then we'll get the ball ready for play right when TV says they're out [of commercial]."

Given the inherently competitive nature of joint practices, it's not unusual for fights between players to break out on the field, which can have dangerous consequences for all involved. However, no such altercations took place with New England and Jacksonville the past two days.   

"It went great," Morelli observed. "It's really interesting when you put two teams together who haven't practiced. Sometimes, they get a little more competitive, but [the Patriots and Jaguars] worked really well together. I compliment both coaching staffs for the preparation and the discipline. You can really see how they have very good control of their athletes. It's excellent."

Year-two leap for Lucien

"Next man up" is one of the Patriots' favorite mottos. Whenever a player is injured or otherwise unavailable, whoever is next in line on the depth chart must step in and is expected to perform at a high level.

Thus far in 2017 training camp, Devin Lucien has been that next man up while fellow second-year receiver Malcolm Mitchell continues to work slowly back from an unspecified injury. In fact, Lucien might be the most pleasantly surprising development for the Patriots this summer. He has made eye-popping receptions, many for touchdowns, almost every day.  

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"With some of the guys getting dinged up, I just wanted to come in and show the coaches I was ready to play," Lucien told reporters, "and that I can do whatever it is they ask me to do, whether it's a catch or blocking. I just want to be ready to go when my number's called."

A member of the 2016 Patriots draft class, Lucien spent his entire rookie season on New England's practice squad, where he gained valuable experience on the scout team.

"The coaches did a very good job of keeping us in the mix during the season," Lucien continued. "We weren't just running [opponents'] plays off cards the entire time. We were able to run our offense still. If you couple that with the fact that you're going up against a Malcolm Butler and the rest of our corners, you just automatically get better while learning the playbook.

"The offseason, though, was a huge time for me to hone in on my plays right before [spring practices] and show the coaches that I could handle the playbook."

Unfortunately, late in Tuesday's joint practice, it appeared that Lucien injured his left hamstring. He spent several minutes trying to jog it off during the last 11-on-11 team period and continued to clutch that area of his leg while conducting post-practice media interviews.

Jags' perspective

It was interesting to hear Jacksonville starting QB Blake Bortles describe his joint practice experience after two days in Foxborough.

"Up front, [the Patriots] single everybody up [on defense]. That's kind of just making everything one-on-one as far as the blocking schemes and then they do a lot of different things in coverage with their safeties.. It's been good going against different looks. It's definitely different than what we see in Jacksonville.

"Butler made a really good play yesterday and picked me off in the two-minute [drill]. I thought that was a really good job on his part. They do a good job disguising coverages. I think schematically they mess with you a little bit and take away different things. They make you think they are taking something away so you go the other way. You have to be sharp in what you are doing pre-snap. They are all really good players and do a good job.

"It's cool to go practice against the defending World Champions," Bortles concluded. "It was about what can we do, how do we react in this situation, how can we continue to get better."

Stock Watch

Buy: Rob Gronkowski – The big tight end was back to his old self, hauling in pass after pass from QB Tom Brady against the Jacksonville defense throughout Tuesday's session.

Sell: Malcolm Mitchell – Though the second-year receiver is slowly increasing his workload in the early portions of practice, he continues to retreat to the rehab field thereafter and has yet to see action in 11-on-11 team periods.

Play of the Day: In one 11-on-11 team period, second-ye zone. QB Jimmy Garoppolo's slightly underthrown pass forced Lucien to readjust his body by spinning 180-degrees backward to make the catch with both defenders draped on ar WR Devin Lucien got behind two Jaguars defenders on a deep corner route to the end him. Lucien still managed to keep both feet in bounds for the score.