Dad04, I too have experience being around and working with elite baseball and softball players. I'm old yet I still swing a bat and hit pretty regularly. But yeah I know, so what.
Confidence comes from knowing your body movement is efficient enough to produce a good swing consistently whether it's golf or baseball. Keyword being consistently. And that consistency feel is fleeting from day to day. Playing defense is much less a consistency problem to solve. Coaches such as Deggs teach body movement efficiency. These guys are hard to find and recruiting them is what keeps players playing at a high level.
Bregman went 1 for 22 after he got called up to the Astros. It was nothing mental, he changed his weight shift and arm action. And all was good after that. Somebody helped him do that.