We can put adverbs and adverb phrases at the front, in the middle or at the end of a clause.
The front position of the clause is the first item in the clause:
Suddenly I felt afraid. Cambridge Dictionary
I notice some writers add comma after adverbs when it is the first item in the clause:
Suddenly, Home Sale Agreements Are Falling Apart Across the U.S. Bloomberg
So, Should I add comma? or Is it matter of writing style?
Suddenly, three cats went out from behind the trash bins, the black, the white and the gray. Ray tried to run away, but the three cats surrounded him.
Is the above statement correct?