Building on some other replies, my son was faced with a similar situation freshman year. He is at a D1 mid-major on the East coast. He was recruited as a hitter – 1B/DH – and the team’s hitting coach was well respected from an MLB family. Son calls home one day and said he is struggling with a change suggested by his hitting coach. I asked the same question as the poster, Why? Son hit .500 plus in top CA league JR/SR HS and had just hit over .350 in limited plate appearances as a true freshman. My initial reaction was to push back. Son explained that coach was trying to close a hole that will be exposed at higher levels, with not much other detail. I was suspect but he pursued the change and it was really humbling and frustrating for him. Summer ball started off horribly and he was ready to revert back to his old swing. Thankfully he didn’t. The following Fall our staff was top 10 in the nation with 4 pitchers drafted or moving to SEC for final year of eligibility. My son called home after a Fall practice and said his hitting coach saved his career. The 81-83 slider was now 87-90 and without the swing change he would be failing. College coaches, especially ones that have been around awhile, know which swings work. Unfortunately, they can’t always articulate the reasons clearly. That said, I suggest listening very carefully. Best of luck to your son.