Angry enough, therefore, to take on again (4)
I believe the answer is:
sore
'angry' is the definition.
('sore' can be similar in meaning to 'angry')
'therefore to take on again' is the wordplay.
'therefore' becomes 'so'.
'to take on' says to put letters next to each other.
'again' becomes 're'.
'so'+'re'='SORE'
'enough' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sore that I've seen before include "Eros (anag.)" , "Wound; painful" , "Tender spot" , "very much" , "To be very old" .)