Victor splitting indigo block (5)
I believe the answer is:
anvil
'block' is the definition.
(anvil is a kind of block)
'victor splitting indigo' is the wordplay.
'victor' becomes 'V' (phonetic alphabet: alpha, bravo, charlie etc.).
'splitting' is an insertion indicator.
'indigo' becomes 'anil' (anil is a kind of indigo).
'v' inserted into 'anil' is 'ANVIL'.
(Other definitions for anvil that I've seen before include "hard block" , "bit off one's ear" , "Heavy metal block in forge" , "Block on which metals are hammered" , "Alvin (anag.)" .)