Replacements may be sparse (6)
I believe the answer is:
spares
'replacements' is the definition.
The definition and answer can be both acts as well as being plural nouns.
Perhaps they are linked in a way I don't understand?
'may be sparse' is the wordplay.
'may be' indicates an anagram.
'sparse' with letters rearranged gives 'SPARES'.
Can you help me to learn more?
(Other definitions for spares that I've seen before include "Is merciful towards, refrains from hurting" , "Lets off; reserve parts" , "Extras with spears" , "Replacement items, like tyres" , "Extras in case of necessity" .)