Rocky and Tennis Ball are shown to be friends in BFDI and BFDIA.
Episodes suggesting a friendship
In "Take the Plunge: Part 1", when given the chance to speak, Rocky called Tennis Ball his "good ol‘ friend".
In "Barriers and Pitfalls", Tennis Ball kicks Rocky so that he doesn't collide with Woody.
In "Don't Lose Your Marbles", Rocky threw up a red ball that Tennis Ball turned in to the Announcer.
In "Return of the Hang Glider", when Pencil announces that Rocky can't barf, Tennis Ball says that's amazing.
In "Get in the Van", Tennis Ball wanted Rocky to win the prize, saying that he wanted Rocky's barf back because he thought that it was cute.
In "A Leg Up in the Race", Rocky barfs on Tennis Ball. Tennis Ball at first thinks he and Rocky will both be unable to climb the ladders when they are the only ones left, but Rocky immediately ditches him by vomiting to the top.
Episodes suggesting a conflict
In "Take the Plunge: Part 1", when Rocky spoke to Tennis Ball, he seemed a bit annoyed.
In "Are You Smarter Than a Snowball?", after Tennis Ball said Rocky should learn how to write with his legs, Rocky kicked him, and seemed happy as Tennis Ball rolls away.