Thanks for your interest in our dictionaries. I think that the first sense of this entry (jugar a la pelota) is actually supposed to refer to this usage. I've made some adjustments to hopefully make this clearer. Changes will be visible once our bilingual dictionaries are updated in the next months.
I added "pepper". It does not apply to tennis as far as I know, and no online sources implied that it would.
However, I haven't found anything on line that would indicate the correct verb for "warm up" in tennis parlance. Perhaps simply "practice". I'll change "play ball" to "practice" and that should be good for now.