Born, bred, and raised in the deep South. Living in the Northeast now. Since I have been a traditional Catholic, I have only had the opportunity once to be in this situation. I had to attend my niece's wedding. They are non-denominational. There was lots of praying, during which I recited a rosary.
I do not know if this was particularly the "right" thing to do, but it is what seemed to be appropriate at the time.
Ordinarily, I would not have attended, but I had to take my mother. I had little other option, so I did the only thing I could think of without making the situation difficult for my mother. At one time during the service, I just walked away as we were outside and it was easy to just move out of view.
I don't know how I would handle the prayers before a baseball game. I don't think stepping aside would be inappropriate. Maybe you could have your son recite a Guardian Angel prayer or something next time. Just a thought, as I often envision my children's Guardian Angels when they are playing like that.
When we were NO in the South, our children were 2 of the 6 children in their entire school that were Catholics. The discrimination didn't really start until about 4 grade--about 9. I imagine that's when children are beginning to hear what their religion lessons and Protestant ministers are telling them.
I remember our oldest coming home from school because the little boy who had been his best friend since 1st grade had decided that my son was not going to heaven and therefore they could not be friends. His friend told him that his name was not written in the "book of life" and could not got to heaven. It was really hard.
We also got a few "hmms" on Good Friday when our children did not go to school or participate in other activities. We also would never allow our children to spend the night with friends on Saturday and go to "church" with their friends. Lots of times I had mothers reassure me that they would take our son to church with them. I had to explain more times that I can count how that would not be acceptable for us.
One really good thing that happened in our NO parish then was getting a "traditional" minded priest. He started this "program" for the children that he called Defenders of the Faith. He taught this class and gave them all questions to study. At the end of the year they had a Jeopardy like quiz, with the winner receiving $100. We helped our boys study. I remember saying to our priest what a great catechism class that was. Funny, because he used the Baltimore Catechism (only I didn't know it then.)
It's hard to be a Catholic in the predominantly Baptist South, but I find it harder to be a traditional Catholic in the predominantly Catholic Northeast....