Run off after second short race (6)
I believe the answer is:
sprint
'short race' is the definition.
(I've seen this before)
'run off after second' is the wordplay.
'run off' becomes 'print' (I've seen this before).
'after' means one lot of letters go next to another.
'second' becomes 's' (common abbreviation).
'print' after 's' is 'SPRINT'.
(Other definitions for sprint that I've seen before include "Rush" , "Run at full speed for a short distance" , "Short race at full speed" , "Short fast run" , "Run quickly" .)