To wreck a boot is simply not allowed (5)
I believe the answer is:
taboo
'not allowed' is the definition.
(I've seen this in another clue)
'to wreck a boot' is the wordplay.
'to wreck' indicates anagramming the letters.
'a'+'boot'='aboot'
'aboot' is an anagram of 'TABOO'.
'is simply' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for taboo that I've seen before include "Socially prohibited" , "Ritually forbidden" , "Not to be mentioned" , "Beyond the pale" , "Social prohibition" .)