1. To slosh and flow over the edge (of something). Be careful that the soup doesn't splash over the side of the pot while you're stirring it. He jumped into the bath and a bunch of water splashed over.
2. To cause some liquid to slosh and flow over the edge (of something). In this usage, a noun or pronoun is used between "splash" and "over." The waves came crashing into the cliffs, splashing foamy water over the top. He jumped into the bath and splashed a bunch of water over the edge.
3. To slosh or spatter onto someone or something. Ice-cold water kept splashing over us as we navigated the treacherous rapids in our kayak. Make sure you put a lid on that pan while you're cooking bacon, or grease will end up splashing all over your brand-new shirt.
4. To cover or drench someone or something with some liquid after sloshing or spattering it onto them. In this usage, a noun or pronoun is used between "splash" and "over." I tripped as I was approaching the table and accidentally splashed wine all over the guests. The whale leaped up and came crashing back down into his pool, splashing water over the entire audience.
splash something (all) over someone or something
to cause a liquid to overflow or engulf someone or something. Tony splashed water all over Nick. Who splashed milk all over the table?
[for a volume of liquid] to overflow its container. A lot of the coffee splashed over before I got to the table with the cup. Don't fill it so full and it won't splash over.