Strong second row (5)
I believe the answer is:
stiff
'strong' is the definition.
(I know that strong can be written as stiff)
'second row' is the wordplay.
'second' becomes 's' (common abbreviation).
'row' becomes 'tiff' (tiff is a kind of row).
's'+'tiff'='STIFF'
(Other definitions for stiff that I've seen before include "Inflexible" , "Not giving" , "Rigid, prim" , "Difficult" , "Starched, rigid" .)