The most common and most likely answer to this crossword clue is the 15 letter word JACK-IN-THE-BOX
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More clues leading to the result JACK-IN-THE-BOX
Buddy explains!
The straight part
We know that "He may spring a surprise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he may spring a surprise = jack-in-the-box.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.
Crossword Answer definitions
JACK-IN-THE-BOX noun- Children’s toy where a figure pops out of a small box.
- A con-man who deceived tradesmen by substituting empty boxes for others full of money.