Ritual performed with zest in battle (10)
I believe the answer is:
austerlitz
'battle' is the definition.
(Austerlitz is an example)
'ritual performed with zest' is the wordplay.
'performed with' is an anagram indicator.
'ritual' mixed up with 'zest' makes 'AUSTERLITZ'.
'in' acts as a link.
(Other definitions for austerlitz that I've seen before include "One of Napoleon's victories" , "Napoleon victory, 1805" , "battle" , "French victory" , "One of 29 dn's battles" .)