It's taken when Reg, being angry, is out to get even (7)
I believe the answer is:
revenge
'get even' is the definition.
'revenge' can be an answer for 'get' (thesaurus). I'm not sure about the 'even' bit.
'it's taken when reg being angry is out' is the wordplay.
'it's taken when' becomes 'even' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'being angry' indicates an anagram.
'is out' means one lot of letters goes inside another.
'reg' anagrammed gives 'rge'.
'even' placed into 'rge' is 'REVENGE'.
'to' is the link.
Can you help me to learn more?
(Other definitions for revenge that I've seen before include "Malicious retaliation" , "Satisfaction taken for injury" , "Ship remembered in verse" , "Retribution" , "An eye for an eye" .)