1. To slosh or spatter up the length of something. Mud splashed up my pantlegs during the hike. The storm kept getting worse, and huge roiling waves splashed up the sides of the cliffs.

2. To cause some liquid slosh or spatter up the length of something. In this usage, a noun or pronoun is used between "splash" and "up." Be careful out there—you're splashing mud up the side of the house! The bacon splashed grease up the wall behind the stove as it cooked in the pan.