I found this baseball… but… it doesn't really look like a baseball?
I started with a quick inspection of the file to determine the file-type:
$ file baseball baseball: ASCII text, with no line terminators
Followed by inspecting the file contents:
$ head baseball TzRaVUNVMlRNRTRIQTZMSFBGWkdTNVpTSzVZVU1ZSllIQk5ER00zREdKTkhBVTJWSkJHVkNWMllPRlVFSzMyRE9GTUVNMkNaR0Y1RU1VUlpNUlNHS1JSWE9CQ1VVU1pZSk4ySEFWVFVPVTJGQzJDV000WlUyUVNHSlpBVFNNUT0=
The content appeared to be encoded so I leveraged CyberChef to perform additional analysis. This challenge was made quite easy with CyberChef's "magic wand" detection, which quickly determined the encoded string was produced with three operations; Base58, followed by Base32, followed by Base64. Reversing the operations produced the flag.