Monsters consequently turning on head of security (5)
I believe the answer is:
ogres
'monsters' is the definition.
(ogre is a type of monster)
'consequently turning on head of security' is the wordplay.
'consequently turning' becomes 'og' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'on' becomes 're' (regarding).
'head of' indicates taking the first letters.
The first letter of 'security' is 's'.
'og'+'re'+'s'='OGRES'
Can you help me to learn more?
(Other definitions for ogres that I've seen before include "Bugbears" , "Fairytale giants" , "Gorse (anag.)" , "Monsters can be goers" , "She-giant of fairy tale" .)