... defeats Nolan in the video game, mocking about it.

[Cat - Man]

Jack always defeats Nolan in the video game, mocking about it.

Is "mocking" grammatically fine here, or some grammatical issue in this sentence?

Context: made it

 

[jutfrank]

As a transitive verb, it needs an object, such as 'him'.

 

[teechar]

@Cat - Man , also note:
1- Nolan is typically a surname, whereas Jack is a first name.
2-

Is "mocking" grammatically fine here

We do not use "fine" in the interrogative or negative forms of such sentences.
Say, for example:
Is "mocking" okay/correct here?

or is there some grammatical issue in with this sentence?

Note especially the verb I added to that clause.

Context: made it I made up that sentence.

See the correction above.

 

[emsr2d2]

Jack always defeats Nolan in the video game, mocking him about it.

Is "mocking" grammatically fine correct here no comma here or and are there some any [other] grammatical issues in this sentence?

Context Source: I made wrote it.

Please note my corrections above.

With the addition of the object "him", the sentence is grammatically correct but it's not very natural. For a start, we tend to use "beat" rather than "defeat", unless we're commentating on professional sport. Also, we'd be more likely to use "and [frequently] mocks him about it". Note that to use "the video game", there would need to be a previous reference to the specific game you're talking about. If you're talking about various games, use the plural without an article.

Jack always beats Nolan at Resident Evil 4 and frequently mocks him about it.
Jack always beats Nolan at video games and frequently mocks him about it.

You didn't give us the context - you gave us the source. Context would be something like "I'm explaining to a friend that Jack always beats Nolan at [name of game] and then makes fun of him about it".