This is usually because the herb is too dry and or the papers is too dry.
It can also be that the joint was too tight, or too loose.
What to do if it runs?
Well, spit on your finger or get some water on it, then wet the run in front of it so it will not run anymore.
Sometimes to help this, when the joint is rolled, the user will take the end they will light, and wet the front half. This adds a little moisture to the paper so it will not run.