In this video guide I will show you how to Win a Quick Race on any track in the Skatepark (not unlockable in Split Screen mode).
First thing is go to the options menu and change the difficulty to easy.
Then go to quick modes and select quick races.
Pick the falsest car you got, then select the first map on Skatepark.
Once you win the race press the A button to get by the finishing results screen and the achievement will pop.
These can also be done during the story progression once the Skatepark maps come up.