Group regularly boycotted Tesla (5)
I believe the answer is:
octet
'group' is the definition.
(group of eight musicians)
'regularly boycotted tesla' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'tesla' becomes 'T' (scientific unit).
The alternating letters of 'boycotted' are 'octe'.
'octe'+'t'='OCTET'
(Other definitions for octet that I've seen before include "Eightsome" , "Musical group" , "Musical composition for eight performers" , "Music for eight" , "What takes members up to eighth" .)