You can play it, a mere bagatelle (7)
I believe the answer is:
pinball
'bagatelle' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for pinball that I've seen before include "It may require tilting when played" , "Slot machine bagatelle" , "Arcade game where a metal sphere negotiates hazards" , "Slot-machine game" , "Electrically operated form of bagatelle" .)