One holding baton, finishing off a biannual event (8)
I believe the answer is:
solstice
'biannual event' is the definition.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for solstice that I've seen before include "it occurs biannually" , "When the sun is at its greatest distance from the celestial equator" , "When the sun is farthest from the celestial equator" , "Shortest or longest day of the year" , "Closest I come to time when sun is farthest from equator" .)