They used to have pro baseball playing out of Puerto Plata, I don't think they do anymore. I think you would have to go to Santiago, which is about an hour and a half away from Sosua. Check here:
http://www.licey.com/
And check out the links page. There might be a schedule someplace there, but you would have to speak a little Spanish to navigate.
As for amateur baseball, you will find lots and lots. If you are staying at the Casa Marina, there are many leagues that play out of the schoolyard very nearby (basically across from it). I think there are games every night...they play until the power goes out...lol. There are also some really good games out of the diamonds by the airport. And a big stadium in POP, but I don't know where you would find out the schedule for this stadium.
Hope this helps!
