He was taking a shot for his Instagram when a passer-by got a little bit irate and began shouting at the veteran news-hound.
In a Guardian blog, Rusbridger said: "He ran down the hill shouting that I had no right to take pictures and I’d better effing delete them. As he got nearer he became a rather large and shouty speck, sweat beading on his bald head as he bellowed in my face."
"We were effing out of order. It was illegal to take effing pictures here and if I didn’t delete the effing picture he’d effing call the police. He was really quite menacing - in the manner, say, of a nineties gangster movie.
"I explained I was disinclined to delete the picture I had taken in a public space just because he looked to be on the point of murdering me. This made the speck even crosser."
Ten minutes later, two police officers showed up to caution Rusbridger and his photographer for a crime they didn't even know they were committing - illegal use of a tripod.
The two police officers were apparently well within the law to give a caution - Rusbridger says it's illegal to use any kind of "photographic stand apparatus" on Hampstead Heath.
There you go, you learn something new everyday.
And the coppers were nice enough to pose for a photo for Rusbridger's blog - no word on whether or not they used a tripod for the shot.