やる気か？だったらさっさと来やがれ！

"You want to fight? If so, then hurry up and come on!" is the translation on Casual Patterns and Slang.
I'm not sure how it comes about.

In my dictionary, やる気 means willingness or eagerness or determination to do something and it was somehow translated as "You want to fight?"
Is 来やがれ the combination of 来る and やがる? 「やがる」 is a verb suffix used to indicate hatred or contempt for the person doing the action, which is explained on the page. What does 来やがれ mean in this context?

What would the whole sentence mean in the natural language other than the translation there on?

やる気 is not a set phrase you found in your dictionary, but that's an expression "verb + 気", meaning "will to do" there. やる is a slangy word for けんかする/戦う "to fight", so the first sentence is a question "Do you have a will to fight with me?", i.e., "You want to fight?".

やがれ is the imperative form of やがる, so 来やがれ is 来い "come on!" with hatred or contempt.

さっさと is an adverbial phrase, so it's more likely "soon/rapidly/immediately".