A Whanganui teenager was "terrified" when a man she didn't know began chasing her in public and yelling incoherently.

The 17-year-old girl was standing outside a Four Square on March 17 last year waiting to be picked up by someone when Bryce Cleeve ran towards her and began yelling, the Whanganui District Court heard on Thursday.

Cleeve, 34, called the girl a "whore" and a "slut" and told her to "come here".

"The victim had no idea who [the defendant] was," Judge David Cameron said.

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The victim "became terrified of the defendant and what his intentions were".

Cleeve continued to yell at the girl and his words "started to become incoherent" as he approached her.

He chased the victim around the block while yelling and screaming at her, Judge Cameron said.

The girl's father arrived and got her to safety.

The man has previous convictions that date from 1999 to 2013.

He pleaded guilty to behaving threateningly. Defence lawyer Debbie Goodlet said Cleeve was "seriously assaulted by the complainant's father" after the incident.

In sentencing, Judge Cameron said he needed to "deter others from terrifying innocent members of the public in this way". He handed Cleeve a two-month community detention sentence with a 7pm-7am curfew.