Ariana Grande's gotta be wondering how an obsessed fan made it all the way to her front door before cops were called to track him down on her property.
Law enforcement sources tell TMZ ... a man in his 20s showed up to the L.A. home of the singer. We're told he brazenly knocked on her door around 2 PM Saturday and asked for her. The property manager who answered the door told the intruder Ariana wasn't home.
Our sources say it's unclear how the man bypassed security measures on the grounds to get all the way to Ariana's house -- but when he did, they called cops. Responding officers found the man near the house, and while arresting, he allegedly spit on one of the cops.
We're told they found a love note to Ariana which included directions to her house. The man was booked for misdemeanor trespassing and felony battery ... for the alleged spitting.
The scary incident comes on the heels of another someone calling 911 earlier this month claiming shots were being fired on Ariana's property.
We were told cops were skeptical because she's been a swatting victim in the past. They still sent cops to check things out and determined it was, in fact, a swatting incident.