Bit out of end of pen ran (7)
I believe the answer is:
nibbled
'bit' is the definition.
(nibbling is a kind of biting)
'end of pen ran' is the wordplay.
'end of pen' becomes 'nib'.
'ran' becomes 'bled' ('bleed' can be a synonym of 'run').
'nib'+'bled'='NIBBLED'
'out of' is the link.
(Other definitions for nibbled that I've seen before include "Took small bites (of something)" , "Took small bites; ate intermittently" , "Pecked" , "Bit off very small pieces" , "Bit off little pieces" .)