Encourage team’s first burst of activity (5)
I believe the answer is:
spurt
'burst of activity' is the definition.
(I've seen this in another clue)
'encourage team's first' is the wordplay.
'encourage' becomes 'spur' (spur can mean to encourage).
'team's first' becomes 't' (1st letter of 'team').
'spur'+'t'='SPURT'
(Other definitions for spurt that I've seen before include "Short spell of increased speed" , "A short burst of activity" , "Gush out suddenly" , "Jet, gush" , "Gush; sudden burst" .)