The sentence is Native Americans originally developed lacrosse what is the word that (originally) modifies

I think it is developed.

Right. Originally modifies the verb

"developed."

The word "originally" modifies the verb "developed" in the sentence. It provides additional information about the development of lacrosse by Native Americans. To identify the word being modified by an adverb like "originally," you can ask yourself what action or state of being is being described or in what manner it is being done. In this case, "developed" is the action being described, and "originally" tells us when this development took place.