The method underpinning entries in Crossword Championship spectacle (5,4)
I believe the answer is:
light show
'spectacle' is the definition.
(thesaurus)
'the method underpinning entries in crossword championship' is the wordplay.
'the method' becomes 'how' (I've seen this in another clue).
'underpinning' means one lot of letters go next to another (in a down clue, some letters go under others).
'entries in crossword championship' becomes 'lights' (I can't justify this - if you can you should believe this answer much more).
'how' put after 'lights' is 'LIGHT SHOW'.
Can you help me to learn more?
(Other definitions for light show that I've seen before include "might be aurora australis" , "kaleidoscopic display" , "Series of moving beams" , "visual display" .)