Springs to mind, initially, as an outburst (5)
I believe the answer is:
spasm
'an outburst' is the definition.
(I've seen this in another clue)
'springs to mind initially' is the wordplay.
'springs' becomes 'spas' (I've seen this in another clue).
'initially' says to take the initial letters.
The first letter of 'mind' is 'm'.
'spas'+'m'='SPASM'
'as' is the link.
(Other definitions for spasm that I've seen before include "Muscle twitch" , "Tic, sudden contraction" , "cramp" , "Sudden muscular contraction" , "sudden movement" .)