This is the most basic
grind trick in
skateboarding. It is easiest learnt (equally easy as a
boardslide).
To perform this trick, approach your grind object at a slow speed and ollie above it. You must bring both of your trucks down onto it, so half the board is on either side, hence the name 50-50. Continue along until you are ready to finish grinding, then simply ollie.
Note: The 50-50 is a very easy grind to ollie as it is flat, others are much harder and require a certain method.