I think baseball is a sport, even though I'm British and we don't play it here. Its more of a sport than...fishing...'OoOoO look at me I'm casting my line OoOoO.'

 There are more facets which make up a sport than simply how much exertion it requires... It also has to do with skill. Under his definition, most of the activities in the Olympics are not sports, since they have only a momentary physical effort. Throwing a javelin, discus, or shot putt require effort only for a moment. Same applies to bobsledding, and many skiing events require much skill, but very little actual physical exertion.

Bricklaying and ditchdigging require a great deal of exercise... But is hardly a sport.

What determines a sport has more to do with competition and skill than it has to do with physical exertion.

 Your European uncle probably also thinks football is played with a round ball.

 Baseball is a sport. If not, then ping pong isn't, bowling, badminton, lawn darts. If you compete to see who wins and who loses, it's a sport.

 If you get payed for it , if there is a professional league for it ( MLB ), and if it has its own tournament in the olympics ( world baseball classic ) . Than it is a sport buddy. Your uncle cleary is a dunce and doesn't know what he is talking about, FYI the star baseball players make
$ 30 million dollars A YEAR!
There is programs for it at the Pro, College, High school, and Youth levels. I believe that 100% considers it a sport.

 Baseball is a sport for sure... What do you call all that running,hitting & throwing??

 How can you say that, baseball is loved by more than just the United States. It is huge in Japan and China as well. It is most definitely a sport!!!!! Especially when people are paid for being professionals, not hobby lovers.

 I think its a sport. I think chess is a sport. I question what team sports are doing on the Olympics as I thought that was meant to be about individual skill but meh.. That's a random thought.

 If your uncle thinks that baseball isn't a sport, then what is a sport in his opinion?

 Baseball is a sport, a hobby is different.