I saw some people on game forums having trouble with killing this spot. An easy way to kill this spot is you move one of the surrounding picnic tables and place it in front of the hubba at the other end of the spot (you start out on the opposite side by default). from there you go back, get some speed and just grind and flip trick the hell out of the table and the hubba or just air down like i did. Only took me a few tries to get the desired score after trying to grind all the curved ledges for what seemed like hours.