Translation:I'm not interested in practicing baseball.
The difference is between jugar an intransitive verb, and practicar a transitive verb. Intransitive verbs do not require a direct object, so "juego" can stand alone as "I am playing." When the subject "tenis" is added, the preposition "a" is needed. The literal translation being, "I am playing at tennis." "Practicar," a transitive verb requires a direct object so a preposition is not used.
Still puzzled, as I've seen too many instances of both using or omitting 'al', or 'a' before the sport. From Spanishdict: Habla constantemente de lo bueno que es jugando fútbol. - He is forever going on about how good he is at soccer. PLUS that example even includes 'at' in English! Google translate for I'm playing tennis is Estoy jugando tenis, and Google translate for I'm playing football is Estoy jugando al fútbol.
I think in the first example, if you translate to english 'he is constantly talking about how good he is at playing', the 'playing' doesnt stand alone, so therefore needs defining, so its intransitive, and so, no 'al'. But when it comes to the rules of which sport gets the 'al' and which doesnt, that has been the topic of much discussion. Just enter into google translate 'i play' then add various things, and you will see that there doesnt seem to be a logical reason to 'al or not to 'al'. Football, soccer, yes. Basketball, tennis, no. Poker, chess, yes.
07/08/18. According to www.spanishdict.com, "practicar" means "to practice" when meaning 'to train' generally or 'to practice' a religon. But with reference to sports, the correct translation is "to play." Here, though similar, the speaker's disinterest in baseball extends not to just practicing the sport, but also to playing it at all.
I'm not sure that makes sense. Practicar=practice was introduced some lessons ago. And just like with English, and I'm guessing, with other languages, words have more than one meaning, depending on context.
Its system can be erratic in grading and correcting. I report when I feel I'm right.
After reading all of the comments, I still don't understand the relevance between to play and to practice when using 'al'.
When I use the word play, I say "I will play baseball today". When I use the word practice, I say "I will practice at baseball" meaning to train at or for baseball. When constructing a sentence, to practice has the "at or for" built in (implied), but when playing, it must be added to the sentence structure?
My translation: I'm not interested in baseball practice.
(My meaning: No me interesa practicar béisbol, pero me encanta jugar en los juegos. / I'm not interested in baseball practice, but I love to play in the games.)
I would greatly appreciate someone explaining to me why my interpretation is wrong -- "I'm not interested in baseball practice." thanks!