All sports involve conflict: one side against another. In many ways sports are symbolic warfare. One side attempts to defeat the other. We call it "winning," but to win is to defeat. And make no mistake about it: the winners feel strength and joy in their victory and the losers feel awful and despondent in their defeat.
In evolutionary terms, we humans have survived to the point of reading and writing here at enotes because of two main factors. One: we cooperated to help each other make it through and/or Two: we cooperated in fighting or fought individually to defeat and kill others. Part of us likes to help, and part of us needs to fight. And sports resonate in that part of us that likes to fight.
It was said above that baseball is not violent. Well, maybe it is not as violent as the gladiators in old Rome's Colosseum, but it is violent in measured and civilized and symbolic ways. The smashing of a ball into the seats, the splintering of a bat, the collision of runner and catcher at home plate, cleats aimed at the shins sliding into second base... all are singular acts of separated violence, and we love it.
And of course baseball, though it has its elements of violence, is mild compared to football, rugby, ice hockey ("I was watching a fight and a hockey game broke out"), boxing, mud wrestling... symbolic wars all of them, and part of us loves it because it's in us all.