When you’re born into baseball, it’s inevitable that something is going to be a little different about how you grow up.

Phillies rookie righthander Mark Leiter Jr. was the kid in Little League who was going for the double play when other infielders would be happy just to make a straight throw to first base because, he says, “when you grow up watching major league games, you expect it to be played the same everywhere.”

He’d already done all the skill drills taught in high school. And when he pitched for the varsity and won a game, instead of a typical congratulation from his dad, former major-leaguer Mark Leiter Sr. might say, “You could have gotten big-league hitters out with what you had today.”

“That was just the scale he was grading things on,” Leiter Jr. said. “It wasn’t forced on me. It was always just part of how we talked about baseball.”

Mark Leiter Sr. made his big-league debut with the 1990 Yankees and played in 11 seasons with eight teams. Leiter Jr.’s uncle is Yankees broadcaster Al Leiter, who began and ended his MLB career with the Yankees but is best known in these parts for the seven seasons he pitched for the Mets.

Leiter Jr. always wanted to go into the family business and has been preparing his whole life, from asking dozens of questions when his dad brought him to the ballpark to dissecting with him every game he played in.

The 26-year-old made a dozen relief appearances in his first call-up from Triple-A this season and, because three starters are hurt, he is in the starting rotation in his second stint with the Phillies. He is 1-0 with a 4.20 ERA. “I’m doing what I always hoped I would do, what I always believed I could do and what I’ve been working toward with my dad’s help,” he says.

advertisement | advertise on newsday

“His passion for the game was there from the beginning,” Leiter Sr. said. “As he got older, our conversations about pitching got more sophisticated and great. We talked about ways to set hitters up, how to drill down on their tendencies. It was like having a teammate as a son.”

Sitting in the third-base dugout at Citi Field on Saturday, Leiter Jr. said, “Getting to the majors is like my dad and I have come around full circle. I grew up on these fields.” He remembers Opening Day at Shea Stadium in 1998, when his father’s Phillies played his uncle’s Mets, “and the next day there was a picture of the three of us in our home newspaper [The Asbury Park Press] shagging flies during BP.”

Leiter Jr. said a famous last name had advantages. “Scouts or [college] recruiters hear the name and sometimes people would come out to see you or take an extra look at you,” he said. “It opens some doors for you, but you still have to back it up and get yourself through the door.”

Out of Toms River North High, Leiter Jr. opted to go to NJIT because of the chance to start right away — “he needed to pitch if he was going to be able to dial it to 90,” his father said — but his profile really turned up on May 3, 2013, when the senior struck out 20 hitters from Chicago State. “I think that was the only game where the Phillies scouted me,” he said with a smile.

After two days of watching the 2013 draft and not hearing his name, father dragged son out for a family golf outing before the third and final day started. There, on the 14th hole, they learned the Phillies — the team Leiter Jr. rooted for after his dad stopped playing — had picked him in the 22nd round.

Mets videos

Leiter Sr. had an inkling something was coming for his son this spring when he pitched 2 2⁄3 innings of relief in a Triple-A game and had eight strikeouts. “I saw the way he pitched and thought he might not be prepared for how things can happen fast in baseball,” he said. “I called him and said, ‘I don’t know when you’ll be called up, but when you punch out eight people, they’ll think you’re ready.’ ”

Three days later, Leiter Jr. was on his way to Citi Field to join the Phillies for the April 18 game against the Mets. He did not get into the game, but his father was outside the clubhouse when it was over. In a long embrace, Leiter Sr. recalled that his son whispered in his ear, “We did it!”

“I told him, ‘No, son, you did it!’ and he said, ‘No, Dad, we did it!’ ” Leiter Sr. said. “He’s so unselfish. To hear ‘we?’ As a father, it just touches your heart.”