Pedant needs to stay alert in the middle (8)
I believe the answer is:
stickler
'pedant' is the definition.
(a pedant is a stickler for detail)
'to stay alert in the middle' is the wordplay.
'to stay' becomes 'stick' ('stick' can be a synonym of 'stay').
'in the middle' means to look at the middle letters.
The middle of 'alert' is 'ler'.
'stick'+'ler'='STICKLER'
'needs' is the link.
(Other definitions for stickler that I've seen before include "Purist" , "Person who insists on something, say punctuality - sounds adhesive" , "Punctilious, insistent person" , "Particular type" , "One insisting on correctness" .)