How can I do a baseball themed room?

Hi there Coach, here is a link to some ideas.

https://thecottagemarket.com/2014/04/baseball-diy-projects.html

Take baseball cards and distress them, yellow em up with some tea bags, use a few use alot, make a collage etc.

Ebay has quite a bit of nostalgic baseball decor available. Wallpaper, tin signs, old baseballs, and posters. You could use some of these items to enhance a nostalgic theme.

Hi ! Is this for a kids room ? Or for a rec. Room ?

A high school locker room

You can also purchase tape that looks like baseball stitching. But depending on where it was applied, it may not be durable enough to withstand 'curious fingers'.