FOXBOROUGH, Mass. -- The methods that have made Bill Belichick one of football’s most successful coaches continue to evolve, and he’s introduced a new one to the mix in 2018: rookies with random, non-permanent jersey numbers in spring practices.

That’s why running back Sony Michel, the first-round pick from Georgia, was wearing No. 51 during Tuesday’s organized team activity.

That number is illegal for running backs to wear in games, per NFL rules (numbers 20-49 are allowed), which highlights the point that Belichick is making to his newcomers.

“Really not too worried about all the important stuff like that -- numbers and what color gloves you wear and all of that,” Belichick said Tuesday. “That’s not really at the top of the list right now. Trying to learn football, trying to become a team, trying to get better each day -- that’s really where our focus is.”

How Belichick brings the team together to achieve that goal is often notable. In past years, he’s had all players practice without any numbers in the spring, a method that forced them get to know each other better and increase their level of communication. Longtime Pittsburgh Steelers coach Chuck Noll did something similar.

But the NFL since has disallowed that practice, so Belichick, as he often does, has come up with a different type of twist.

Hence the reason rookie quarterback Danny Etling (seventh round, LSU) was wearing a red, noncontact No. 58 jersey at Tuesday’s practice. That wouldn’t be allowed in a game.

“My first-ever football number in school was 28, so that’s the closest I’ve ever got to it,” Etling said of the unusual number.

All draft picks had numbers in the 50s on Tuesday -- Nos. 56 (Andre Tippett) and 57 (Steve Nelson) were off limits because they were once owned by Patriots Hall of Famers -- while undrafted players had numbers in the 60s and 70s.

So it was unusual to see Braxton Berrios, the receiver from the University of Miami selected in the sixth round, wearing No. 55.

And then there was one example of how the bizarre numbers actually seemed to affect the play on the field. When quarterback Brian Hoyer looked downfield and saw running back James White running with a defender wearing No. 59, he liked the matchup because that’s usually the number donned by a linebacker. But as Hoyer delivered a high-arcing throw to the back right of the end zone, he soon realized that No. 59 was rookie cornerback Keion Crossen, the seventh-round pick from Western Carolina who flashed his 40-inch vertical leap and intercepted the pass.

Players wearing No. 59 usually don’t jump that high.

Just as running backs like undrafted Ralph Webb of Vanderbilt usually don’t wear No. 68, while undrafted punters like Corey Bojorquez usually don’t wear No. 71.

It’s yet another version of Belichick’s outside-the-box coaching methods.