Had problem with small run (4)
I believe the answer is:
dash
'run' is the definition.
(I know that dash is a type of run)
'had problem with small' is the wordplay.
'problem with' is an anagram indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'had' mixed up with 's' can make 'DASH'.
(Other definitions for dash that I've seen before include "Rush - elan" , "Morse feature" , "Dart" , "Run quickly - little taste - hyphen" , "If you're smart, you'll cut one" .)