Momof3,
In the context of college baseball recruiting, ff a Coach is asking your son to apply ED typically there is a reason. The coach wants a committed athlete and the athlete is getting help with Admissions that he wouldn't ordinarily get and a spot on the team. I would verify your understanding with the coach.
Each situation and school is different with their academic requirements and the number of ED slots available for athletes. In addition, ED is a time when the applicant pool has some flexibility with regards to athletes and non-athletes. I know in my oldest son's case the overall acceptance rate was 30% for ED and about half that for Regular Decision for the University overall. Caveat: each college (architecture, engineereing, etc...) within the University can make their own admission decisions and the acceptance % can be much lower than the overall University. In my middle son's case (non-athlete) he was a borderline candidate for the school he most wanted to attend. He applied ED also, and he's doing extremely well in the college of engineering. ED acceptance can lock you if accepted, but it can give you an academic boost as well into a very competitive school..