I lived not far from Placentia, actually right on the Placentia/Yorba Linda border. As far as I know there is no Crook Park in Placentia. There's Wagner, which is behind an elementary school by El Dorado High School, Koch Park, not far from there, Tri-City, and another park that's name I can't remember.
Definitely NO Crook Park. Don't bother looking, you won't find it
Actually, the only park I have managed to find that has Crook in the name is Hilda Crooks park, nowhere near Placentia.
I believe whoever posted this is talking about Koch Park, which I know is known for strange activity, as in little wanna-be gang bangers and drug deals. Not a place you wanna be in after dark.