What is the meaning of 「そーれっ」 I am reading a manga and two characters are playing badminton. They take turns hitting the birdie, and each time they hit it, they say. This word is actually in the WWWJDIC dictionary, with a definition of "oof; umph; whoosh". There was also a note in the margin of the English transliteration of the manga I found that said it's like a happy grunt. I am still a little confused. I think I have heard (or a variation of it) used as a way of saying, "take that!", like a form of smack talk when doing some kind of move. How does relate to this? Is it really like a happy grunt, or is it more like smack talk?

or (same difference) is a sound made, similar to 'oomph', 'here you go', and 'take that', normally made when hitting something. Happy or not depends on context. Manga margin translations are probably not the most reliable of sources.