Yes Golf is considered to be a sport.
Golf is a legitimate sport because it is highly competitive, requires mental capacity, and demands physical extortion and muscle use.
Golf is seen as just a game, but golfers are highly competitive.
In any sport you just have to play one day, but in golf a tournament may be up to four days that you have to play.
Golf fulfills the definition of a sport.
According to Merriam-Webster, a sport is "a contest or game in which people do certain physical activities according to a specific set of rules and compete against each other."
There's no doubt golf fulfills that definition, especially the part about the rules.