Wiktionary
vb. (present participle of drop in English)
Wikipedia
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.
Usage examples of "dropping in".
The bread dough had risen impossibly, was spread all over the counter and dropping in large chunks onto the floor.
There were a fair number of people out tonight, dropping in on neighbors or heading for parties or whatever.
Maybe you think those 'heads will keep their cool without me dropping in one each group every once in a while?
Coll did have to admit that he was asking for far more detailed explanations than he needed to, but he noticed that Dicea kept dropping in on Dirk from time to time with one unnecessary question after another, so he felt justified.
Suddenly we were falling, dropping in utter darkness as if the world had disappeared from beneath our feet.