Opening popular with one chess champion going round India (7)
I believe the answer is:
initial
'opening' is the definition.
(I've seen this before)
'popular with one chess champion going round india' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'with one' becomes 'i' (Roman numeral. I am not sure about the 'with' bit.).
'chess champion' becomes 'tal' (Mikhail Tal, i936-i992).
'going round' means one lot of letters goes inside another (some letters go around others).
'india' becomes 'i' (phonetic alphabet: alpha, bravo, charlie etc.).
'tal' enclosing 'i' is 'tial'.
'in'+'i'+'tial'='INITIAL'
Can you help me to learn more?
(Other definitions for initial that I've seen before include "Word's first letter" , "First home, corgi, ultimately, wagging tail" , "Letter - opening" , "Occurring at the beginnng" , "Sign" .)