"My father likes basketball."
Translation:A mi padre le gusta el baloncesto.
the website studyspanish.com/grammar is an excellent place to get answers to questions like this. Others have suggested this site at points when I've had exactly these kinds of questions, and the site has proven to be terrific. The section on 'The Personal A" should answer your question. That's where I went to after my previous post, and the answer was both clear and helpful.
Duolongo drives me nuts with things like this. The structure 'A mi ... le gusta' is given absolutely NO justification. It is just dropped on you with no explanation. Maddening.
This is what is called "The Personal "A"". It is used when you are referring to a specific person as the subject of a sentence. There is no English equivalent so it can be confusing. I found this very quick video to be useful: https://www.youtube.com/watch?v=JPNWu61BAtQ
"Se" only replaces "le" when there are two pronouns in a sentence. So, if "basketball" were implied by previous conversation, you could say "A mi padre se lo gusta."
I agree, I hardly think "a" is necessary since there's no confusion as to who is liking basketball.
Le is the third person objective pronoun, referring to the father. I find it helpful to think of gustar as translating as "to provide enjoyment" rather than as "to like;" that makes it easier to understand which noun affects the conjugation and which affects the preceding pronoun.