Ben Coulbeck, 28, was walking home from the shops through Lovell Park when a heavy police presence was in place.
The 16-year-old boy is said to be in a serious condition in hospital following the incident, which West Yorkshire Police were called to at 2pm on Thursday.The boy was found with stab wounds in the park, which is just off North Street.
Forensic officers combed the scene for evidence and a short time later the cordon was reduced in size, but a bench within it was covered by officers.
Mr Coulbeck lives just a few hundred yards from the scene of the incident, and described seeing the scene as 'shocking' and 'worrying'.
He told the YEP: "I've never seen anything like this around here before.
"I've never seen any problems on the park before - never anything of this magnitude.
He said that the fact this incident had taken place in broad daylight next to a busy road was "shocking".
"I've lived in this area for around three years now," Ben added. "I've always thought there might be some trouble knowing what the area is like, but I've never seen anything like this.
"It's mad, I use this park quite a lot to get into town and it's usually alright, even at night, but the cordon is a bit worrying."
A spokesman for West Yorkshire Police said: "Anyone who witnessed it or who has any information that could assist the investigation is asked to contact Leeds District CID via 101 quoting crime reference 13180508838 or call the independent charity Crimestoppers anonymously on 0800 555 111."