Hammers southern shelves (7)
I believe the answer is:
sledges
'hammers' is the definition.
(I know this)
'southern shelves' is the wordplay.
'southern' becomes 's' (abbreviation).
'shelves' becomes 'ledges' ('ledge' can be a synonym of 'shelf').
's'+'ledges'='SLEDGES'
(Other definitions for sledges that I've seen before include "Snow carts" , "Sleighs; hammers" , "More than one big hitter" , "insults" .)