Dropping in is a skateboarding trick with which a skateboarder can start skating a half-pipe by dropping into it from the coping instead of starting from the bottom and pumping gradually for more speed. When a skateboarder drops in, they use their gravitational potential energy to gain initial velocity, allowing the skater to skate longer before exhausting himself and thus to take more runs.
When a skateboarder drops in, they stand on the deck of a half-pipe, put their back foot on the tail of the skateboard, and push it so that the back wheels just roll over the coping into a position like in a tail stall. They then put their front foot on the deck, which now hangs over the half-pipe, lean forward, and start skating the half-pipe.
Dropping in is an essential skill for anyone who wishes to skate a half-pipe efficiently, but it is also a very intimidating trick because it requires falling face down from a high place. It is very typical that when a skateboarder tries to drop in for the first time they fall on their back because they are too afraid to lean enough forward. The most important things to think of before dropping in