In America, we don't generally use singular sport to refer to sports in general. AndyNZ's first example sentence, "She was good at sport during her school years" would sound strange to us. I would have interpreted the given sentence to refer to a particular unspecified sport. "He did not like the sport" (of skiing, for example). How would one say that in Spanish, if 'el deporte' refers to all/some sport? Would it just depend on context?
I agree that if I was talking about someone as a spectator I would probably say 'he does not like sport' but if I was talking about someone as a participant I think I would be more likely to use the plural 'he does not like sports'. i.e. The school boy doesn't like (taking part in) sports.
Probably because "sport" and "sports" can mean the same thing in English. "She was good at sport during her school years" or "She was good at sports during her school years". I associate the former with Commonwealth countries, the latter with the US. Though YMMV...
BTW, your question should begin with "Why are both...", not "is". Just for future reference...
'A él ' clarifies the indirect object 'le', which could mean 'to him/her/it'. 'El deporte' is the 3rd person singular subject of 'gusta'.
Remember gustar is used 'backwards', more like to be pleasing than to like. So technically, think of it as "to him, sports are not pleasing (to him)", but don't actually translate it that way.
Kind of - when using an indirect object (like le, les), the le is always required. "A él" is optional, and would clarify who le is referring to. It could be "a él", "a ella", "a Judy" - "le" is still required, but "a (someone)" is just icing.
With direct objects (since you mentioned lo), "lo" or "la", it's a little different, because lo/la is only sometimes required. But for here, just recognize that "le" is an indirect object, and "lo/la" are direct objects.
Yes, the "a el", " A mí" etc. is both for clarity and for emphasis.
In addition, DL generally likes the redundancy with "gustar" That is, generally begin with "A él" or "a ellos". Etc.
Though it is not always necessary in Spanish, nevertheless, for DL, you should automatically put it in.
Different grammar structures for "gustar" and "like" in both languages:
A ella (indirect object) no le gusta (intransitive verb) el fútbol (subject).
If we change the subject from singular to plural we need to change the verb: A ella no le gustan los partidos
She (subject) does not like (transitive verb) football (direct object).
In English, sports or sport is the direct object of the transitive verb like. But Spanish doesn't have a verb that is commonly used in this situation that corresponds to like. Gustar means "to be pleasing to." The subject and object are reversed with respect to "like" in English.
So, in the Spanish sentence, le, which is clarified by a él, is the indirect object of the verb gusta and el deporte is the subject. (Gustar also is one of many verbs that have the quirk of taking indirect objects instead of direct objects. So, in this sentence in Spanish, there is no direct object.)
'Gustar' isn't a reflexive verb and doesn't use the subject pronouns 'yo, tu, etc'. It actually means 'to be pleasing', so you have to say 'it is pleasing to me/to him/etc.' 'It is not pleasing to him', as in this sentence, is 'no le gusta'. As the 'le' here could be 'to him/her/you', 'a él' is placed before the pronoun to clarify. 'A él no le gusta el deporte' is expressed in English as 'He does not like sport'.
A software limitation, I suspect. The further you take your answer from a literal translation of the phrase, (i.e. paraphrase), the less likely the software will recognise it as a valid answer.
For example, "The dude's not into sports" has the same meaning ultimately, but the software comparison database is unlikely to recognise "dude" or "into" in the context of what it expects to get from you, so gives a "wrong" response.
OTOH, a human marker might accept it.
'to like' means 'find agreeable, enjoyable, or satisfactory.' 'pleasing' means 'satisfying or appealing.'
They're virtually identical in meaning. As for the rest, there is no 'how we speak English' -- English is spoken in many countries across the world, and there are wild variations in usage.
As far as I can tell, there is no issue with the grammar of 'Sports are not pleasing to him.' and the answer should be accepted.