Wickedly excited yell about boundary (6)
I believe the answer is:
evilly
'wickedly' is the definition.
('evilly' can be a synonym of 'wickedly')
'excited yell about boundary' is the wordplay.
'excited' indicates anagramming the letters.
'about' is an insertion indicator.
'boundary' becomes 'vi' (type of boundary in cricket, roman numerals).
'yell' is an anagram of 'elly'.
'elly' enclosing 'vi' is 'EVILLY'.
(Other definitions for evilly that I've seen before include "In a very wicked manner" , "With wicked intent" , "In wicked or depraved way" , "Extremely wickedly" , "in a bad way" .)