Is paintball a sport

Definition by the dictionary
SPORT:
an activity involving physical exertion and skill in which an individual or team competes against another or others for entertainment.

So I would say yes.

Not sport

It certainly can be. There are professional competitions and sponsors. But most people just do it for fun. Go out with a group of friends and team up and shoot the hell out of each other out in the woods/desert/country. Some people even make big elaborate courses to play on. My friend had one with little bunkes made out of shipping containers and towers we built and building we made from old shipping pallets. Our friends dad owned an international shipping company/firm. So we just got all this crap for free and made a gigantic paintball course/bmx/dirt bike course. It was sick. We had Burms build up on the sides of the shipping containers and you could use the 4 packs as fox holes sorta.... I bet it's still there to this day being used by kids in our neighborhood. We built that thing to last.

Coming from a guy who used to compete in professional paintball tournaments, yes, it is a sport.

We would train every Wednesday as well play matches every weekend. We came first in our first amateur tournament as well as came third in our first professional tournament.

In the end though it got really expensive and our team had to disband.