One holding shortened baton in biannual event (8)
I believe the answer is:
solstice
'biannual event' is the definition.
(the winter and summer solstices)
'one holding shortened baton' is the wordplay.
'one' becomes 'sole' (synonyms).
'holding' means one lot of letters goes inside another.
'shortened baton' becomes 'stic' (I can't explain this - if you can you should believe this answer much more).
'sole' enclosing 'stic' is 'SOLSTICE'.
'in' is the link.
Can you help me to learn more?
(Other definitions for solstice that I've seen before include "Seasonal turning point" , "Time of year when sun is furthest from equator" , "Shortest or longest day of the year" , "21 June or 22 December?" , "Closest I come to time when sun is farthest from equator" .)