Procedure of one exercise class on field (6)
I believe the answer is:
recipe
'procedure' is the definition.
(thesaurus)
'one exercise class on field' is the wordplay.
'one' becomes 'i' (Roman numeral).
'exercise class' becomes 'pe' (physical education).
'on' says to put letters next to each other.
'field' becomes 'rec' (short for recreation ground).
'i'+'pe'='ipe'
'ipe' after 'rec' is 'RECIPE'.
'of' is the link.
(Other definitions for recipe that I've seen before include "Cook's instructions" , "Set of instructions for preparing a dish" , "Directions for cooking the turkey e.g." , "List of ingredients" , "Food method" .)