Commotion about soldiers backing attrition (7)
I believe the answer is:
erosion
'attrition' is the definition.
(thesaurus)
'commotion about soldiers backing' is the wordplay.
'commotion' becomes 'noise' (I've seen this in another clue).
'about' indicates putting letters inside.
'soldiers' becomes 'OR' (Other Ranks).
'backing' shows that the letters should be reversed in order.
'noise' enclosing 'or' is 'noisore'.
'noisore' reversed gives 'EROSION'.
(Other definitions for erosion that I've seen before include "Abrasion" , "Process of wearing away, by water or time" , "A wearing away as of rock by water" , "Disintegration" , "Mechanical process of wearing something down" .)