Occasion seeing millions enthralled by deadlocked match (4)
I believe the answer is:
time
'occasion' is the definition.
(I've seen this before)
'millions enthralled by deadlocked match' is the wordplay.
'millions' becomes 'm' (abbreviation).
'enthralled by' is an insertion indicator ('enthral' can mean 'capture').
'deadlocked match' becomes 'tie' (match with no winner).
'm' inserted within 'tie' is 'TIME'.
'seeing' acts as a link.
(Other definitions for time that I've seen before include "Pub closing call" , "Age" , "Great healer, so they say" , "It's measured by watch or clock" , "See 15" .)