Upsetting fit old dad more, he's moderate (6-2-3-4)
I believe the answer is:
middle-of-the-road
'moderate' is the definition.
(I've seen this before)
'upsetting fit old dad more he's' is the wordplay.
'upsetting' indicates anagramming the letters.
'fit'+'old'+'dad'+'more'+'he'='fitolddadmorehe'
'fitolddadmorehe' with letters rearranged gives 'MIDDLE-OF-THE-ROAD'.
(Other definitions for middle-of-the-road that I've seen before include "Safe" , "Average" , "Avoiding extremes; moderate" , "place for dangerous drivers?" , "Unexciting" .)