"Is Gambling A Hobby?" is the wrong question, the question should be "Can Gambling Be A Hobby?" and the answer is yes, it surely can. A hobby is something that you do often as you like doing it, and it can be anything. A hobby can be a sport, reading, writing, watching TV, playing video games, or anything in general including gambling because you do it either everyday or very often and you like doing that thing.
If you are gambling for fun, you have gambling as a hobby, and if you gamble because you are addicted to it or you do it to earn money from it, then maybe it isn't a hobby but it's something you are forcing yourself to do not because you like doing it but because you want to get something out of it.
This is just a matter of perception and habits in running things in this world, gambling is an object just like the other fields you said such as soccer, watching, reading, writing, drawing playing games is just an object and you can freely do it and consider it for your own interests whether it is made as a job or hobby or whatever it is.
Yes, someone to find entertainment in gambling, of course, he makes gambling a place as a hobby, and makes it a place to make money, meaning that you force gambling as a place for you to work, just like playing soccer, writing, reading, playing games, many people make it a job, this is quite possible to do also in gambling, even though we consider it wrong if gambling is considered a job but it is quite possible for someone to do it, and that's where the logic lies to conclude the opinion that gambling is a hobby or not in someone's life.
The issue of whether or not it is addictive is relative, just like the other fields we mentioned, we can get addicted to that field.