Baseball and Microphone don't seem to have a stable relationship, as Microphone is loud, obnoxious, and short-tempered, while Baseball is prone to arguing with her, but the fact that both are on the same team does not seem to help.
Episodes suggesting a friendship
In Breaking The Ice, both end up on the same team, and when Baseball comes to greet them, he is very enthusiastic, saying it "all happened so fast".
In Marsh on Mars, Microphone volunteers to save Marshmallow, and Baseball allows her to go as long as she doesn't yell.
Episodes suggesting a conflict
In Marsh on Mars, when Baseball asks for volunteers to go into the rocket, Microphone volunteers very loudly, which angers Baseball.
In A Kick in the Right Direction, Baseball first tells Microphone that she should be the goalie, saying that her "loudness" has caused her to mess up challenges. Microphone disagrees with this, but thanks to Suitcase, she reluctantly follows. When arguing with Dough, she neglects to keep the ball out of the goal, angering the Grand Slams. Baseball yells at her and tells her she should be further from the competition and makes her play another position, earning an aggravated response from Microphone.
In Let 'Er R.I.P., Baseball tries to give her advice, but she ignores him with an annoyed expression, a sign she doesn't care.