Tweak soft part of foot (5)
I believe the answer is:
Here is my best explanation:
'tweak' is the definition.
('pinch' can be a synonym of 'tweak')
'soft part of foot' is the wordplay.
'soft' becomes 'p' (musical abbreviation for 'piano').
'part of foot' becomes 'inch' ('inch' is part of 'foot').
(Other definitions for pinch that I've seen before include "Steal (informal); squeeze", "Steal (colloq.); one felt by the poor", "Grip sharply; steal", "Squeeze between the fingers", "appropriate", "A little", "amount of salt?", "Tweak", "Economise - steal" and "Appropriate".)