Forfeits regularly encountered worry constantly (4)
I believe the answer is:
fret
'worry constantly' is the definition.
'forfeits regularly encountered' is the wordplay.
'regularly encountered' indicates alternate letters.
The alternating letters of 'forfeits' are 'FRET'.
(Other definitions for fret that I've seen before include "Worry; sort of saw" , "Wear; guitar ridge" , "worry its way through?" , "Display anxiety" , "Part of a Gibson, say" .)