In the year 1991, Donald Trump witnessed a mugging from his limousine. He told his driver to pull over, got out, confronted the attacker, and caused him to stop.
I googled this a bit, and found an article in The Epoch Times describing this event. The source of the article is another news article on Philly.com. Unfortunately, the Philly.com article is behind a pay wall.
There also appears to be a picture of a New York Daily News article being circulated.
Evidence In Support
There is that news article and the image. The Epoch Times is a real paper, and the articles writer still works there. According to Wikipedia, the author of the article (James Rosen) did write such an article, though the source it cites doesn't confirm that, just that such an article was being circulated during the 2016 election.
Some details make sense, for example Paula Abdul did indeed perform in the Meadowlands Arena at that time; then called the Brendan Byrne Arena.
No major outlets seem to have discussed this story, even those friendly to the president. A Google image search shows both a white and yellow version of the article, with the exact same cropping. The article says there is no police report. The New York Daily News doesn't have a stellar reputation.