Forty-nine in the red are angry (5)
I believe the answer is:
riled
'angry' is the definition.
(I've seen this before)
'forty-nine in the red are' is the wordplay.
'forty nine' becomes 'i' (I can't justify this - if you can you should believe this answer much more).
'in the' indicates putting letters inside.
'red' becomes 'r' (I've seen this in other clues).
'are' becomes 'led' (leading is a kind of being).
'r'+'led'='rled'
'i' put within 'rled' is 'RILED'.
Can you help me to learn more?
(Other definitions for riled that I've seen before include "Annoyed" , "Cross" , "Made angry" , "Nettled" , "Vexed" .)