“Beat on the Brat” was described by Dee Dee Ramone as a true story.

Joey saw some mother going after a kid with a bat in his lobby and wrote a song about it.
- from Please Kill Me: The Uncensored Oral History of Punk by Legs McNeil and Gillian McCain

Joey himself, however, related it to a desire to attack a spoiled middle class child.

When I lived in Birchwood Towers in Forest Hills with my mom and brother, it was a middle-class neighborhood, with a lot of rich, snotty women who had horrible spoiled brat kids. There was a playground with women sitting around and a kid screaming, a spoiled, horrible kid just running around rampant with no discipline whatsoever. The kind of kid you just want to kill. You know, ‘beat on the brat with a baseball bat’ just came out. I just wanted to kill him.
- The Ramones by Nicholas Rombes (33 1/3)