User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-7336553-20130321170949/@comment-5020152-20130322122532

Pinning is a new monster mechanic introduced in 3rd Gen games. If you are pinned, Dung Bombs work great. If you're using a Hammer, then you can also try to aim for the head and make the monster stagger.

By the way, it's always nice seeing a new MH fan. Good luck on MH3U!