For example, leader of group, chief boffin (7)
I believe the answer is:
egghead
'boffin' is the definition.
(I've seen this before)
'for example leader of group chief' is the wordplay.
'for example' becomes 'eg' ('e.g.' can be a synonym of 'for example').
'leader of' indicates taking the first letters.
'chief' becomes 'head' ('head' can be a synonym of 'chief'**).
The initial letter of 'group' is 'g'.
'eg'+'g'+'head'='EGGHEAD'
(Other definitions for egghead that I've seen before include "Cracked" , "Intellectual (sl.)" , "scholar" , "Very clever person" , "Brainy type" .)