Men lose it badly in important event (9)
I believe the answer is:
milestone
'important event' is the definition.
'men lose it badly' is the wordplay.
'badly' indicates anagramming the letters.
'men'+'lose'+'it'='menloseit'
'menloseit' with letters rearranged gives 'MILESTONE'.
'in' is the link.
(Other definitions for milestone that I've seen before include "Wayside indicator" , "Roadside distance marker" , "Significant event or stage - a measure" , "Important stage (reached)" , "Pillar" .)