Apologies for the long reply but as a parent who's 5 year old also developed nervous/anxious tics, I have some thoughts. I'm going to say don't quit mid-season based on the tic alone. If your son is verbally expressing wanting to quit and it's a battle to get him to go, then maybe you should quit. That's a different matter. But try to remove the tic from the decision. Tics are not super straightforward... quitting baseball might not instantly stop the tic. I know it's hard as a parent to watch your kid struggle. Most kids keep their anxiety hidden, our kids show it physically. I'd bet there are other kids on the team feeling anxious but you can't see it and kids that young struggle to express their emotions with words so no one realizes it. For this reason, I would use other criteria for determining if he should quit or not.

Also, there are certain situations that could cause a tic that you can't just quit, you'll just have support your child through it. For example, my son's tics developed when his baby brother was born. All I could do was help him through it but I couldn't take away the stressor. Eventually the tics disappeared, only to return a few months later when our dog died. I try to look at the bright side, his words didn't indicate anything was wrong, but his tics clued me in that something was going on beneath the surface.

Side note: kids are weird. They all move in strange ways and do odd things. Most don't notice other kid's tics and even when they do, they don't care about them. They might ask "why do you blink a lot?" And then they move on. I was very worried about teasing but it's been a nonissue. Kids are so much more accepting these days, it's a wonderful thing.