The most common and most likely answer to this crossword clue is the 6 plus 2 letter word CHANGE UP
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "Go from first to second" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case go from first to second = change up.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CHANGE UP mean?
CHANGE UP noun- A pitch thrown with the arm motion of a fastball, but which travels at a much slower velocity because it is released without the fingers adding power to the delivery.
- (by extension) An unexpected event.