Grace regularly seen in fantastically surefooted, outstanding performances (5,2,5)
I believe the answer is:
tours de force
'outstanding performances' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'grace regularly seen in fantastically surefooted' is the wordplay.
'regularly seen' indicates alternate letters.
'in' is an insertion indicator.
'fantastically' indicates an anagram (a fantastical ordering of the letters).
The alternating letters of 'grace' are 'rc'.
'surefooted' anagrammed gives 'toursdefoe'.
'rc' inserted inside 'toursdefoe' is 'TOURS DE FORCE'.
Can you help me to learn more?
(Other definitions for tours de force that I've seen before include "masterpieces" , "Masterly feats" , "Great feats" .)