Unfortunately let pop fall over (6)
I believe the answer is:
topple
'fall over' is the definition.
(topple can mean to tumble or fall)
'unfortunately let pop' is the wordplay.
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
'let'+'pop'='letpop'
'letpop' is an anagram of 'TOPPLE'.
(Other definitions for topple that I've seen before include "Overbalance and fall headlong" , "Knock off perch" , "Overthrow, cause to fall" , "Fall, tumble" , "dethroned" .)