A study score, about 201, by chance (12)
I believe the answer is:
accidentally
'chance' is the definition.
(thesaurus)
'a study score about 201 by' is the wordplay.
'study' becomes 'den' (term for a study or office).
'score about' becomes 'tally' (synonyms. I am not sure about the 'about' bit.).
'a0t' becomes 'cci' (I've seen this in another clue).
'by' says to put letters next to each other.
'den'+'tally'='dentally'
'dentally' put after 'cci' is 'ccidentally'.
'a'+'ccidentally'='ACCIDENTALLY'
Can you help me to learn more?
(Other definitions for accidentally that I've seen before include "Inadvertently, by chance" , "Not purposefully, by mistake" .)