FORT MYERS, Fla. — Two hours before his major league debut last September, Triston Casas sunbathed shirtless in the right field grass at Fenway Park. It was part of a unique, regimented routine he had developed in 2019 and carried through every step of the minors. Changing things up just because he was in the majors wasn’t an option.

Out of earshot of Casas, a veteran Red Sox pitcher walked out of the dugout, saw the scene in right field and bristled. To no one in particular, he made his feelings known.

“Are you (expletive) kidding me?” the pitcher asked.

For Casas, who played 27 games at the end of last season and will take over as Boston’s full-time first baseman in 2023, the learning curve behind the scenes was just as steep as the one on the field. It wasn’t just about learning to hit major league pitching or adjusting to a rigorous travel schedule for the season’s final month. The eccentric Casas had to make significant adjustments to his routine in an effort to fit in.

Throughout September, veteran players took issue with Casas’ pregame routine, which included pregame naps in the clubhouse in addition to the sunbathing. Those veterans, on numerous occasions, voiced their displeasure. There were, in Casas’ words, “clashes” about how he should act. Looking back, the 23-year-old is glad some older players put him in his place because it means they cared.

“I would have been more concerned if they weren’t saying anything to me,” Casas said. “I felt like that would have meant they didn’t feel like I was going to be (in the majors long). I think the fact they were telling me stuff, the fact they were getting on me for the little things meant that they wanted me to go about things the right way. They wanted me to make sure that I’m going to carry on that tradition throughout the years when I stay up here.”

For the eccentric Casas, who has made headlines with his random tweets and red painted fingernails in recent months, major league life represents something of a balancing act. Like all rookies, Casas wants to conform to clubhouse norms by following the examples set by older players and ruffling as few feathers as possible. But he also wants to be himself. Those two things don’t always jell.

“I want to go with the flow. I don’t want to go against the grain. I don’t ever want to be an outlier on the team,” Casas said. “And I think that my play definitely reflects that on the field.

“Off the field, I am who I am,” he said. “My personality is always going to be authentically unapologetic and I am who I am away from the field. When it comes to the field and I step in between the lines, I know I mean business and everybody else knows that I do, too.”

Casas developed his meticulous pregame routine in 2019, his first full-season as a professional. While at Single-A Greenville, the former first-round pick found that he felt more energetic after getting sun before games. After the sunning came a 30-minute nap that began about 90 minutes before first pitch. Often, Casas would lie down in front of his locker and snooze on the floor. He carried the routine throughout his minor league career, from the alternate training site in 2020 to Worcester in 2021 and 2022.

No one in the minors ever took issue with it. Things were different in the big leagues where, as Manager Alex Cora said, players police each other.

“I would just throw down a towel, one over my eyes, one for my head, cross my arms and have people step over me,” Casas said. “Coaches saw me for years. Plenty of coaches, plenty of players, plenty of rehab guys. Nobody ever told me anything. So naturally, I assumed it was OK.

“Getting up to the highest level, realizing that it’s not, that was OK with me,” he continued. “I understood the perspective that there is a little more turnaround in the locker room in terms of media, in terms of cameras, in terms of other things that there isn’t in the minor leagues. I would find a more respectful spot of everybody’s space than in the locker room.”

On numerous occasions, veterans loudly expressed their displeasure with Casas’ routine. That caused tension within a clubhouse that was playing out the string of a last-place season. Casas’ tact was to do what young players have done for decades and not be seen or heard. He tried not to speak to veteran players unless they spoke to him first. Sometimes, tensions boiled over.

“If I ever felt like they were trying to make an example out of me, there would be a little bit of a clash because at that point, I would be considering that disrespect,” Casas said. “But if I know they had good intentions by what they meant, or what they were trying to tell me, then I would definitely oblige and just say yes and keep moving forward because their respect means a lot to me.”

Casas made changes to his routine by the end of last season and will continue to do so in 2023. While he declined to get into specifics, it’s safe to say he won’t be napping in the middle of the clubhouse next season and that his sunbathing sessions will likely be out of public view. Casas didn’t mind compromising in an effort to fit in.

“I couldn’t just scratch everything and then try to build a new routine,” he said. “So there were times where I had to compromise with my teammates and meet in the middle and see how I can incorporate things that I needed to do and things that they thought were disrespectful. I had a certain way of doing things. And I found out when I came here some of the things that I was doing just needed an adjustment in terms of the timing or the location.

“I have a purpose for everything that I do. I think everybody in here understands how meticulous I am about the game, about my routine, about how much pride I take in doing this. So everybody knows that. If I’m doing something, it’s for a reason, and I think everybody respects that. Within reason, I will always compromise with anybody who has a request to make an adjustment to my routine.”

With so much turnover on the roster, Casas will be tasked with getting to know a whole new group of veterans that includes Justin Turner, Kenley Jansen, Corey Kluber and Adam Duvall. Though parts of his first month in the big leagues weren’t easy, Casas looks back fondly and what he learned — both on and off the diamond.

“We had a lot of good individuals on the team and they were all very fair with me,” he said. “More than anything, I just wanted them to be understanding of my situation because they had already all been through it.”

WHEN THE RED SOX take the field to open their spring training exhibition schedule this weekend, fans will get their first look at one of the most radical aesthetic changes in franchise history — the addition of a MassMutual advertisement on each player’s jersey sleeve.

The jersey patch is a central part of a larger 10-year partnership between the Red Sox and MassMutual, which is reportedly worth $17 million per year and will make the Springfield-based bank the club’s signature sponsor. Yet while the patch is a massive change, it’s also likely to be the last we’ll see for the foreseeable future.

For the third consecutive year the Red Sox are sticking with the same rotation of uniforms, which include the club’s traditional home white and road grays plus three alternates, a home red, a road blue and the Boston Marathon-themed yellow City Connects. The Red Sox will also continue wearing a “Boston” variation of their home whites on Patriots Day, as they have since the aftermath of the marathon bombings in 2013.

Red Sox CEO Sam Kennedy said this week they are not currently considering any uniform changes beyond this year either.