Casino big shots — they may rock the boat! (4,7)

I believe the answer is:

high rollers

'casino big shots' is the definition.
(a high roller bets or gambles a lot of money)

I don't understand how the remainder of the clue works.

(Other definitions for high rollers that I've seen before include "Those spending rashly" , "They gamble recklessly" .)

I've seen this clue in The Times.

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