Cut out physical activity without hesitation (6)
I believe the answer is:
excise
'cut out' is the definition.
(thesaurus)
'physical activity without hesitation' is the wordplay.
'physical activity' becomes 'exercise' (I've seen this before).
'without' suggests deleting specific letters.
'hesitation' becomes 'er'.
'exercise' with 'er' taken out is 'EXCISE'.
(Other definitions for excise that I've seen before include "Cut out; commodity tax" , "Internal tax" , "Tax on certain goods and commodities" , "Type of tax" , "that wretches hatefully collect" .)