Police say youngsters using the Noble's Park skate park could have been put in danger.
Officers are condemning vandals who caused damage, sometime between Sunday lunchtime and Monday morning.
Sharp nails and planks of wood were used in an attempt to increase the size of the ramps, causing damage and making the area dangerous.
There's an appeal for witnesses and anyone who can help the investigation is asked to ring Police Headquarters on 631212 or the anonymous Crimestoppers line, on 0800 555 111.
'Unnecessary' delays left electricity customer in limbo
Drone users reminded not to fly devices during Classic TT and Manx Grand Prix course closures
'The Island needs to be able to compete' against other destinations
Public urged to consult on capacity