(1) Harry’s broom had given a wild jerk and Harry swung off it. He was dangling from it, holding on with only one hand. (Harry Potter and the Sorcerer's Stone)
(2) The stupid man swung off the enemy side. (From a Korean English-Korean Diction-ary)
I guess ‘off it’ (1) is the result of ‘swung’ and meaning ‘dangling from it.’ While in ‘swing off’(2), ‘off’ means away from the original place; and the result of ‘swing off’ is ‘the enemy side.’ Is this right understanding?
In the first example, to "swing" is to move while or as if suspended from some central axis. Like a playground swing, where you move back and forth while hanging from a bar. "Off" here is an adverb meaning "away from" or "in a manner resulting in no longer being atop". So Harry is sitting on a broom and holding onto it, and he then moves in a swinging motion that results in him no longer being on the broom. I picture him holding on to the broom with one hand and moving in a semi-circular arc.
The second example is less clear. Is this an isolated sentence used as an example in a dictionary? It's very odd wording. We can talk of "swinging off" something in a literal, physical sense like in the first example. We often use the word "swing" metaphorically to describe someone going between two ideas, like "Jack swung back and forth between loving Sally and hating her". I would read that sentence to mean that the "stupid man" had taken the side of the enemy in some conflict, but now he has swung back to "our" side. But I've never heard someone use the phrasing "swing off a side" in the sense of a side in a conflict. You could say he "swung off the side of the building", but "swung off the enemy side", well, I think I understand the metaphor, but it just sounds awkward.
I would be careful of using Korean examples for correct English usage in general. Where English is concerned, the Korean culture seems more concerned with getting the point across than with getting the grammar correct. This is changing; Koreans are realizing that touting the quality of their goods and massacring our language while doing so creates a bit of a mixed message. (Back when I was managing a computer store, I recall receiving a flyer from a company in Korea that sold printed circuit boards. At the top of the flyer was the header "BEST QUALITY IS ALWAYS WHAT WE CONCERNED." I didn't buy any of their printed circuit boards.)
The site that FumbleFingers provides is a case in point. It purports to be a study site for English and yet it is full of beginner's errors.
