A flash flood?
A five-letter word for sudden movement is probably "start." Make sure the "d" is correct.
boom
One choice is the word ambush.
The letters do not spell any valid 7 letter scrabble word. The letters can be used to spell the 6 letter words nudies, sudden and undies.
The word punitive if defined simply basically means "punish". So to take sudden punitive action would be to take sudden disiplinary action essentially.
jerk, jolt
Concupiscence is a desire or will to do action. Antecedent concupiscence precedes an act of will without being willfully stimulated. Meaning before an action is carried out, there is a sudden desire to do this action.
Impromptu is the closest to spontaneous word. It is a word representing sudden action.
Paroxysm means sudden attack.
Crash is a 5-letter word that can refer to "a sudden noise".
unexpected or sudden
"A sudden turn."
armadillos are easily frightened by sudden action or movements, and also loud, sudden noises
Sudden or unexpected appearance; an unforeseen occurrence; a sudden occasion., An unforeseen occurrence or combination of circumstances which calls for immediate action or remedy; pressing necessity; exigency.
Exacerbation - a sudden worsening in the severity of the signs or symptoms.
Paroxysmal