My son is a 2019 and plays football and recently committed to a D1 for baseball at his dream school (that is a story for another day). We heard lots of encouraging stuff about multi-sport athletes, but where the rubber hits the road baseball coaches want you to focus on baseball and football coaches want you to focus on football. That's just the way it is, and you can't blame an intense coach for wanting to win. So the player needs to be firm in his commitment and tune out the noise when he's missing workouts, etc.
A couple of observations...
The high school he goes to matters. My son's high school is small and relies on the better athletes to play multiple sports, so the culture is supportive. Larger high schools in the area really lean hard on players that try to play multiple sports and it's not pleasant or productive. You should be able to find out about the high school sports culture before you decide where to go.
Communicate with the coaches early. My son told his travel coach in the spring that he was playing football starting in August and would not be doing any travel tournaments after that time. He also told the football coach that he'd be missing 7 on 7 tournaments in the early summer.
Football turned him into a much better baseball player. The time in the weight room, pushing sleds and going head-to-head on the football field transformed him into a physical beast.
There's a price to pay. My son missed out on big recruiting events in the summer/fall following his freshman year and I think it hurt, or at least delayed, his recruiting. Many of his travel teammates were getting offers and committing while he was playing football sophomore year. My son was not on anyone's radar and wasn't getting any love from PG or AC games.
Know what you want your future to be. Once he decided that he wanted to play baseball in college, he made a decision that he was not going to play football his junior year so he could focus on baseball recruiting. For months in the spring of his sophomore year he took pressure from football teammates and coaches but he held his ground. He had a great summer/fall his junior year and his baseball recruiting activity really picked up. He showcased at ~20 colleges, went to several school camps, played Jupiter and other high profile tournaments. He made the best of his time off from football. This turned out to be good timing since he wanted higher academic schools and the schools he was talking to wanted ACT/SAT scores and junior year transcripts, so it set the table for his rising senior summer where things came together.
His senior year (now) he's gone back to football and is having the time of his life. Because of what he's done on the baseball field he's one of the most respected kids on the football field. It's kind of cool to see. I get nervous that he could get hurt, but on the other hand you only live once, and high school football is a pretty unique experience that I wouldn't want to deprive him of. He hits and throws a couple times a week after football practice and plays scout ball on Sundays, and taking a bunch of AP classes. A full life for a high school kid.