"I went outside to go look for my cat who had gotten out earlier and when I went outside I opened the door... I thought it was a German Shepherd at first, I was like 'oh, somebody's dog,'" Kerrisk said.
"Then I looked and it turned back and looked at me, and I was like, 'oh my God no, that's a mountain lion.'"
Timothy noticed the big cat appeared to have its eyes on some children playing on their bikes.
WATCH: Video shows mountain lion lurking on front steps of Pacifica home
He tried to alert them. "And so I started yelling for the kids to go back inside and that's when the mountain lion turned around, saw me coming at like, and started coming at me and then jumped over the fence," he said.
The mountain lion wasn't about to leave so Timothy decided he better do something and try to protect the children.
"He was hiding under the truck so I was like 'I better go outside and get in between him and the kids.'"
The kids were apparently the second thing the mountain lion had its eyes on.
Timothy learned his own cat was definitely on the dinner menu, but managed to escape.
"My neighbor across the street has video of the same cat chasing my cat, my little cat, across the yard under the truck over the bushes and then down the hill, and it comes back five minutes later and that's when he starts watching the kids."
VIDEO: What to do if you come face-to-face with a mountain lion