Caught messing with a fir dealer? One may be unstable (4,7)
I believe the answer is:
free radical
'may be unstable' is the definition.
I can't judge whether this definition defines the answer.
'caught messing with a fir dealer? one' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'messing with' is an anagram indicator.
'one' becomes 'a' (a thing is one thing).
'fir'+'dealer'+'a'='firdealera'
'c' anagrammed with 'firdealera' gives 'FREE RADICAL'.
Can you help me to learn more?
(Another definition for free radical that I've seen is " One may be charged".)