Rocking Clawmark Hill! - S20.E15

Ash and Professor Kukui notice that the Rockruff that lives with Professor Kukui is disappearing at night and returning the next morning badly injured. Following it, they find out that Rockruff is participating in a secret Pokémon training ground. Ash decides to help Rockruff train. Rockruff learns to use Rock Throw. After Rockruff defeats a Magmar that previously defeated it, Professor Kukui decides to leave Rockruff in Ash's care and Ash catches Rockruff.