If you're growing cannabis plants indoors, you may run into an issue where your plant grows so tall that it hits your ceiling. In order to prevent that, many growers will "top" their marijuana plants.
Mr.C Growin4B uploads videos of his indoor garden to YouTube on a weekly basis. He grows cannabis plants in a very small space so he frequently needs to top his plants. For the technique he uses, he takes the top of the plant and pulls down the uppermost leaf growth. He then pinches off the remainder of the top of the plant. In his video below, he explains the process and shows off his technique.
Check out his video here: