The adjective in this sentence is "fast"; "really" acts as an adverb.
There is no adjective in that sentence. The word "fast" is sometimes used as an adjective, but in this sentence it modifies the verb "run," so "fast" is an adverb.
fast ball
Yes. Example: He bought a fast car. Fast is an adjective describing car.
That black horse is running fast.
big
I ran really fast today. Cars go really fast.
Yes, "fast" can function as an adverb. In this context, it describes the manner in which an action is performed, such as in the sentence "She runs fast." Additionally, "fast" can also be an adjective, as in "He is a fast runner."
I RANT REALLY FAST
It can be either, because there is no adverb form (fastly) for speed.A fast car (adjective)He drove fast (adverb)
no, fast is an adjective.
He could do arithmetic in his head *really fast. *optional
Speedy is a specific adjective