Run in seaside area is an offence (6)
I believe the answer is:
breach
'an offence' is the definition.
(I know that breach is a type of offence)
'run in seaside' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'in' is an insertion indicator.
'seaside' becomes 'beach' (a beach is found by the seaside).
'r' going within 'beach' is 'BREACH'.
'area is' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for breach that I've seen before include "Opening - quarrel" , "Gap in a wall or barrier" , "Open up" , "Gap (in defensive wall)" , "Opening -- infraction" .)