Baseball falls in Class 28, toys & sporting goods, and depending on what exactly you sell it can also fall in Class 41 or Class 25 or Class 20. Everything below is read from the USPTO's own list of accepted descriptions, not from an opinion about where it belongs.
Searching the USPTO Trademark ID Manual for baseball returns 69 accepted descriptions, and most of them sit in Class 28. The manual is the list of identifications the office has already approved, so wording taken from it is pre-approved and settles the class at the same time.
The class follows from the identification you write, so "what class am I in" is really "what exactly do you sell". How the class system works covers the rest.
Toys, games, or sporting and exercise equipment.
33 accepted descriptions in the manual mention baseball. For example:
You teach, train, publish, coach, or provide entertainment, events, or media content.
13 accepted descriptions in the manual mention baseball. For example:
Clothes, shoes, or hats.
9 accepted descriptions in the manual mention baseball. For example:
Furniture, mattresses, mirrors, or picture frames.
4 accepted descriptions in the manual mention baseball. For example:
Baseball appears in 4 classes because what you make, what it is made of and the service of selling it are separate classes. Pick the descriptions above that match what you actually do.
Making baseball is Class 28; a shop or online store that sells it is retail store services (Class 35), and a business that does both files in both.
Toys, games and sporting goods: video game consoles and toy guns are here. The game you download is not: downloadable video game software is Class 9.
The class decides what a registration covers; it does not decide whether the name is available. Relatedness is judged on the identifications, so a conflict can sit in a class you never looked at: the same name in a different industry.
Check whether your name is clear for baseball Searches the live USPTO register, including sound-alike and meaning-alike names. First search $2, then $5.Baseball sits in Class 28, toys & sporting goods. That is where the USPTO's own ID Manual puts it: 33 accepted descriptions mentioning baseball fall in Class 28. Depending on exactly what you sell it can also fall in Class 41 or Class 25 or Class 20.
You file in every class you actually use the mark in, and the USPTO charges its fee per class. Selling a product and also running an online store for it is two classes, not one. Filing in classes you do not use is worse than filing in too few: an application has to be supported by real use or a genuine intent to use.
No. The class decides what a registration covers. Availability turns on whether someone already holds a similar mark for related goods, and relatedness is judged on what the identifications say rather than on the class number, so marks in different classes can still conflict.
Not what you sell? Search the class finder for your own wording, or browse all 45 classes.