Perform strongly, mostly, making peg (5)
I believe the answer is:
dowel
'peg' is the definition.
(a dowel is a wooden peg)
'perform strongly mostly' is the wordplay.
I cannot really see how this works, but
'perform' could be 'do' (both can mean complete an action) and 'do' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'making' is the link.
Can you help me to learn more?
(Other definitions for dowel that I've seen before include "Peg used for fastening two adjacent parts of a structure" , "Lowed (anag.)" , "Peg fitting into hole" , "Peg for joining wood" , "Peg to hold two pieces together" .)