Warning: treadle right out of skew! (3,5)
I believe the answer is:
red alert
'warning' is the definition.
(I've seen this before)
'treadle right out of skew' is the wordplay.
'right' becomes 'r' (common abbreviation).
'out of skew' is an anagram indicator (letters skewed or distorted).
'treadle'+'r'='treadler'
'treadler' is an anagram of 'RED ALERT'.
(Other definitions for red alert that I've seen before include "Serious warning" , "Scarlet warning of imminent danger?" , "State of readiness for imminent threat" , "Danger signal" , "Warning signal" .)